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Why does a rocket have to go 25,000 mph to escape Earth?

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theconversation.com – Benjamin L. Emerson, Principal Research Engineer, School of Aerospace Engineering, Georgia Institute of Technology – 2025-01-13 07:34:00

A SpaceX Falcon 9 rocket with its Crew Dragon capsule launches from Cape Canaveral, Fla., in January 2024.
Chandan Khanna/AFP via Getty Images

Benjamin L. Emerson, Georgia Institute of Technology

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.


Why does a rocket have to go 25,000 mph (about 40,000 kilometers per hour) to escape Earth? – Bo H., age 10, Durham, New Hampshire


There’s a reason why a rocket has to go so fast to escape Earth. It’s about gravity – something all of us experience every moment of every day.

Gravity is the force that pulls you toward the ground. And that’s a good thing. Gravity keeps you on Earth; otherwise, you would float away into space.

But gravity also makes it difficult to leave Earth if you’re a rocket heading for space. Escaping our planet’s gravitational pull is hard – not only is gravity strong, but it also extends far away from Earth.

Like a balloon

As a rocket scientist, one of the things I do is teach students how rockets overcome gravity. Here’s how it works:

Essentially, the rocket has to make thrust – that is, create force – by burning propellant to make hot gases. Then it shoots those hot gases out of a nozzle. It’s sort of like blowing up a balloon, letting go of it and watching it fly away as the air rushes out.

A bird's eye view of a rocket blasting off.
On July 16, 1969, a Saturn V rocket sent Apollo 11 and three American astronauts on their way to the Moon.
Heritage Images/Hulton Archive via Getty Images

More specifically, the rocket propellant consists of both fuel and oxidizer. The fuel is typically something flammable, usually hydrogen, methane or kerosene. The oxidizer is usually liquid oxygen, which reacts with the fuel and allows it to burn.

When going into space and escaping from Earth, rockets need lots of force, so they consume propellant very quickly. That’s a problem, because the rocket can’t carry enough propellant to keep thrusting forever; the amount of propellant needed would make the rocket too heavy to get off the ground.

So what happens when the propellant runs out? The thrust stops, and gravity slows the rocket down until it gradually begins to fall back to Earth.

A diagram that shows a satellite orbiting the Earth.
A rocket provides the spacecraft with a sideways push (right arrow), gravity pulls it toward Earth (down arrow), and the resulting motion (red arrow) puts the spacecraft into orbit (yellow path).
ESA/ L. Boldt-Christmas

Fortunately, scientists can launch the rocket with some sideways momentum so that it misses the Earth when it returns. They can even do this so it continuously falls around the Earth forever. In other words, it goes into orbit, and begins to circle the planet.

Many launches intentionally don’t completely leave Earth behind. Thousands of satellites are orbiting our planet right now, and they help phones and TVs work, display weather patterns for meteorologists, and even let you use a credit card to pay for things at the store or gas at the pump. You can sometimes see these satellites in the night sky, including the International Space Station.

An Atlas V rocket took NASA’s Perseverance rover to Mars.

Escaping Earth

But suppose the goal is to let the rocket escape from Earth’s gravity forever so it can fly off into the depths of space. That’s when scientists do a neat trick called staging. They launch with a big rocket, and then, once in space, discard it to use a smaller rocket. That way, the journey can continue without the weight of the bigger rocket, and less propellant is needed.

Against a blue sky, a rocket shoots off into space.
The launch of a SpaceX Falcon 9 rocket from Cape Canaveral, Fla., in May 2024. The rocket carried 23 Starlink satellites into low Earth orbit.
Joe Raedle via Getty Images

But even staging is not enough; eventually the rocket will run out of propellant. But if the rocket goes fast enough, it can run out of propellant and still continue to coast away from Earth forever, without gravity pulling it back. It’s like riding a bike: build up enough speed and eventually you can coast up a hill without pedaling.

And just like there’s a minimum speed required to coast the bike, there’s a minimum speed a rocket needs to coast away into space: 25,020 mph (about 40,000 kilometers per hour).

Scientists call that speed the escape velocity. A rocket needs to go that fast so that the momentum propelling it away from Earth is stronger than the force of gravity pulling it back. Any slower, and you’ll go into an orbit of Earth.

Escaping Jupiter

Bigger, or more massive, objects have stronger gravitational pull. A rocket launching from a planet bigger than Earth would need to achieve a higher escape speed.

For example, Jupiter is the most massive planet in our solar system. It’s so big, it could swallow 1,000 Earths. So it requires a very high escape speed: 133,100 mph (about 214,000 kilometers per hour), more than five times the escape speed of Earth.

But the extreme example is a black hole, an object so massive that its escape speed is extraordinarily high. So high, in fact, that even light – which has a speed of 370 million mph (about 600 million kilometers per hour) – is not fast enough to escape. That’s why it’s called a black hole.


Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.The Conversation

Benjamin L. Emerson, Principal Research Engineer, School of Aerospace Engineering, Georgia Institute of Technology

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The Conversation

Is capitalism falling out of favor? We analyzed 400,000 news stories to find out

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theconversation.com – Jay L. Zagorsky, Associate Professor of Markets, Public Policy and Law, Boston University – 2025-01-13 07:35:00

Choose one.
Fokusiert via Getty Images Plus

Jay L. Zagorsky, Boston University and H. Sami Karaca, Boston University

Capitalism, communism and socialism are the world’s three major economic systems. While the phrase “economic system” may seem like a yawn, countless people have fought and died in major wars over which one should dominate.

Shifts from one system to another, like the 1989 fall of communism in much of Eastern Europe, changed the lives of millions. And while researchers know that a country’s economic system dramatically impacts people’s living standards, less is known about how attitudes toward these systems have changed over time.

We are professors working at Boston University’s new Ravi K. Mehrotra Institute, which is trying to understand how business, markets and society interact. Given many recent criticisms of capitalism, we were surprised to find positive sentiment toward capitalism is slowly rising over time.

The main economic systems explained

Capitalism, communism and socialism are economic and political systems that differ in their principles and organization. Capitalism emphasizes the private ownership of resources and the means of production, driven by profit and market competition, with minimal government intervention.

Communism, on the other hand, advocates for a classless society where all property is communally owned. In communism, wealth is distributed according to need and there is no private ownership, which aims to eliminate inequality and oppression.

Socialism falls between these extremes. It focuses on the collective or state ownership of key industries and resources. This allows for some private enterprise, with the aim of reducing inequality through social welfare programs and obtaining a more equitable distribution of wealth.

Modern economies blend capitalism with socialism to address challenges like inequality, market failures and negative externalities, like when a business harms the environment. Governments intervene through regulations, welfare programs and public services to tackle issues like pollution and income inequality. This creates what economists call a “mixed economy.”

The amount of state involvement varies from country to country. At one end is market capitalism, where markets dominate with a limited government role. The U.S. is one such example.

At the other end is state capitalism, like in China, where the government directs economic activity while incorporating market elements. The goal is to combine market efficiency and innovation with measures to contain capitalism’s social and economic costs.

How to measure people’s attitudes toward economic systems

Some surveys have asked people directly how they feel about these systems.

For example, the Pew Research organization’s most recent survey on the issue found the proportion of Americans with positive views of either capitalism or socialism has declined slightly since 2019, with capitalism remaining more popular overall. Nevertheless, Americans are split sharply along partisan lines. About three-quarters of Republican voters have positive views of capitalism, compared with less than half of Democratic voters.

Unfortunately, there are no long-running surveys tracking people’s feelings toward the three systems. Because of this shortcoming, we used artificial intelligence to analyze references to the three systems in more than 400,000 newspaper articles published over a span of decades.

We identified every news story that discussed capitalism, communism or socialism using ProQuest’s TDM Studio. ProQuest has digitized almost all the articles in major English-language newspapers – including The Wall Street Journal and The New York Times – starting in the mid-1970s, with partial archives from earlier years.

The AI model was designed to assess the tone of each article across several dimensions, including anger, surprise and happiness. After the model scored each article on those qualities, we combined the emotions into three categories: positive, negative, and neutral or unknown. For example, an article discussing capitalism might be rated as 60% positive, 20% negative and 20% neutral.

Using an AI large language model allowed us to track shifts in press attitudes over time – which, to be fair, might not match popular opinion.

How views have changed since the 1940s

When we looked at newspaper articles from the end of World War II to the present, we found something unexpected. In the 1940s, capitalism was not well regarded. The average article containing “capitalism” or “capitalist” got a 43% negative and 25% positive sentiment score. This is surprising, since we looked at newspapers published primarily in countries with capitalist systems.

However, just because capitalism didn’t get a high positive score doesn’t mean that newspaper writers loved communism or socialism. In the 1940s, articles with those words also got relatively high negative scores: 47% on average for articles containing “communism” or “communist,” and a 46% negative rating for “socialism” and “socialist.”

Since that time, however, positive sentiment toward capitalism has improved. In the 2020s, the average article with capitalism got a more balanced 37% negative and 34% positive sentiment score. While capitalism clearly isn’t loved in the press, it’s also not disparaged as much as it was just after World War II.

The news media’s attitudes toward capitalism improved more than attitudes toward socialism or communism over time. In the 1960s, positive attitudes toward all three were roughly the same. Today, however, positive sentiment toward capitalism is 4 or 5 percentage points higher than the other two. The climb wasn’t steady, since the number of favorable articles about capitalism fell during recession years.

Still, some contemporary commentators fret that capitalism is in crisis.

Not long ago, The New York Times – a newspaper located in the world’s financial center – ran an op-ed headlined “How Capitalism Went Off the Rails.” A recent book review in The Wall Street Journal, a newspaper that is a bastion of capitalism, starts, “Our universities teach that we are living the End of Times of ‘late capitalism.’”

But while capitalism clearly isn’t beloved by all, we didn’t find evidence that it’s being overtaken by socialism or communism. Instead, using AI to process the attitudes reflected in thousands of newspaper articles, we found that people – or at least the press – are slowly warming to it.The Conversation

Jay L. Zagorsky, Associate Professor of Markets, Public Policy and Law, Boston University and H. Sami Karaca, Professor of Business Analytics, Boston University

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What the dead, the uncanny and the monstrous tell us about human nature

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theconversation.com – Jue Liang, Assistant Professor of Religious Studies, Case Western Reserve University – 2025-01-13 07:34:00

A scroll illustrating the realm of the hungry ghosts, one of the six realms in Buddhist cosmology.
Kyoto National Museum via Wikimedia Commons

Jue Liang, Case Western Reserve University

Uncommon Courses is an occasional series from The Conversation U.S. highlighting unconventional approaches to teaching.

Title of the course

Ghosts, Zombies and Monsters: What We Fear and Loathe in Religions

What prompted the idea for the course?

I am an expert in Tibetan Buddhism, women and gender, but not in ghosts, zombies and monsters. However, my experience teaching introductory courses on Asian religions and religious studies prompted me to grapple with the challenge of teaching students the importance of understanding the people whom we feel are “other” and come to terms with things that do not make sense.

These fearsome, “other-than-human” beings live on the boundaries of our moral, social and emotional imagination, and they often embody the issues, concerns, hopes and fears that have shaped our lives. Therefore, they are the ideal pedagogical candidates to challenge one’s preconceived notions of death, self and the other.

What does the course explore?

The course is divided into three thematic sections. First, we reflect on ghosts, examining how different cultures provide specific definitions of death and imaginations of an afterlife. We read about Buddhist hungry ghosts, or “pretas,” and Chinese ghost stories. We also explore discussions of hauntings in a Thailand airport as well as the experience of ghost hunters in North America. Ghosts are often believed to be beings who failed to transition to an ideal afterlife and linger in a liminal state, interacting with and haunting the living.

Second, we examine zombies. These are considered another type of liminal beings who are regarded to be alive but have lost the distinct stories that make each of them a unique individual, according to scholar of monster theory Jeffrey Jerome Cohen. We explore the Haitian origin of zombies and the phenomenon of the “uncanny valley,” the eerie feeling we may experience when encountering something that appears almost human but not quite.

Last, we look at monsters. Monster theories and the study of monstrous beings as a cultural category have grown into a flourishing field of inquiry in recent decades. This has opened many avenues for exploring beings typically regarded as categorically different from humans.

The class explores monsters as disastrous animals, gendered beings, exiles from their religious communities and names evoked in news reports to describe individuals who have committed particularly disturbing crimes. We ask questions such as why some animals are more likely to be seen as frightening or malicious than others, and what is gained and lost by calling someone a “monster.”

Why is this course relevant now?

Ghosts, zombies and monsters are as ancient and as contemporary as the humans living with them. We will probably never stop fearing, being disgusted by or projecting some people among us as “monsters.” However, at a time when fear, disgust and labeling carry unusual weight in shaping relationships in our own community, I believe critically reflecting on how we engage with difference and otherness is an urgent call. Monstrous and demonic beings also ultimately occupy a place where boundaries are constantly pushed and redrawn. What was monstrous once might be no longer now, and vice versa.

What’s a critical lesson from the course?

This course brings to the fore what is commonly demonized, marginalized or unseen in religious traditions across the globe, and it asks what it is about ghosts, zombies and monsters that appalls and arrests us. One lesson students take away from the course is that our fears and horrors are always culturally and contextually specific. In other words, ghosts, zombies and monsters are also reflections of ourselves.

What materials does the course feature?

We watch three films, one for each section: Masaki Kobayashi’s “Kwaidan,” Jordan Peele’s “Get out” and Penny Lane’s “Hail Satan?

Students also become familiar with a variety of narratives – both serious and humorous – about ghosts, zombies and monsters, ranging from “Strange Tales from a Chinese Studio,” a collection of supernatural stories, to Key & Peele sketches about Satan or the zombie apocalypse, and Haruki Murakami’s short story “Super-Frog Saves Tokyo.”

Key & Peele.

What will the course prepare students to do?

Good storytelling plays a crucial role, as it allows us to temporarily inhabit another, imagined world. Many of my students revealed their talent for storytelling during a class session where we went around the room sharing spooky tales. In the act of telling each other stories, we begin to understand and navigate our differences.

Students are not going to become professional demon tamers or ghost hunters after this class. Instead, I hope they leave with a newly found recognition, if not tenderness, toward creatures and things they originally were afraid of or felt repulsed by.The Conversation

Jue Liang, Assistant Professor of Religious Studies, Case Western Reserve University

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Secretary of defense must perform a ‘delicate dance’ between the president, Congress and the public

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theconversation.com – Evelyn Farkas, Executive Director, McCain Institute, Arizona State University – 2025-01-11 08:56:00

The U.S. military is a massive group effort serving the nation’s – and the public’s – interests.
AP Photo/Alex Brandon

Evelyn Farkas, Arizona State University

Senate confirmation hearings are slated to begin on Jan. 14, 2025, for Pete Hegseth, whom President-elect Donald Trump has chosen to serve as the next secretary of defense. It’s a massive job, broadly affecting Americans’ security at home and abroad and overseeing huge numbers of people and immense amounts of money.

The Conversation U.S. asked Evelyn Farkas, a longtime Defense Department leader who is now executive director of the McCain Institute at Arizona State University, to explain what the secretary of defense’s job entails and what makes a person effective at that job. During the Obama administration, Farkas was a deputy assistant secretary of defense with a focus on Russia, Ukraine and Eurasia. Prior to that, she was a civilian adviser to the top military officer in NATO, and earlier still she was a senior staff member of the Senate Armed Services Committee, which oversees the military. She also served as a professor at the U.S. Marine Corps Command and Staff College.

What does the secretary of defense do?

They’re responsible for about 3.4 million people, including 1.2 million active duty service members and 1.3 million reservists, as well as about 900,000 civilian employees. The secretary is responsible for making sure those people are able to do their jobs – which, collectively, is to defend the United States, the American people and U.S. interests.

They’re responsible for defense policy, spending and operations, which includes the people, property and equipment at about 500 military bases across all 50 states and another 750 or so bases in 80 countries around the world. They’re responsible for budgeting and spending almost US$2 trillion a year in federal funds, which is about 16% of the overall federal budget.

An overview of a large five-sided office building.
The Pentagon is the headquarters for the U.S. Defense Department.
AP Photo/Charles Dharapak

What is the secretary’s role in commanding the nation’s military forces?

The president is the commander in chief and decides when and how to use the military. But the president’s decision to use force relies on advice and recommendations from the secretary of defense and the chairman of the Joint Chiefs of Staff. The president orders the secretary to carry out military operations, and the orders pass down from the secretary to the relevant commanders from there.

What is an average day or week for the secretary of defense?

The secretary sets the vision and tone for the Department of Defense and helps the president develop his or her defense strategy, and then implements that strategy. The secretary also designs and implements policies to advance the strategy and the overall national security objectives of the president.

The Defense Department’s responsibility is focused on the use of the military, whether it’s to deter attacks or defend American interests. The secretary must make sure the military is equipped and trained – ready – to fight and win the nation’s wars and to conduct any other operations, such as humanitarian, counterterrorism or peace operations.

The secretary sets priorities, which are reflected in the department’s budget. The budget has to be negotiated with Congress, of course. Day to day, the secretary is holding meetings with people who are charged with managing different aspects of the department’s activity. This happens regularly in the Pentagon or when the secretary visits military units and installations in the U.S. or around the world.

There are undersecretaries for policy and the budget and other functions such as personnel and readiness. Then there are service secretaries, who look at all of those issues but only for one specific service – the Army, the Navy, which includes the Marine Corps, and the Air Force, which includes the Space Force.

People stand in rows wearing shirts that say 'Army.'
Prospective soldiers stand in a training formation.
Scott Olson/Getty Images

Does the president talk to the secretary of defense regularly?

It depends on the president. Most presidents have regular meetings with their top officials as a Cabinet, as a group, and then, of course, individually. Some presidents will have a standing lunch with their Cabinet members, or just a formal meeting.

Generally speaking, most presidents would seek to have a meeting at least once a week that involves their secretary of defense. There’s a lot going on in the world, and most of the events or crises involve some decision about the use of military force or some effect on defense capabilities.

How does the secretary of defense affect regular Americans’ lives?

The secretary’s involvement in a decision to use nuclear weapons would certainly affect almost every American. So that’s one way, and any decisions involving war could potentially affect any given American.

Short of that, the economic ripple effects of decisions the secretary makes could be national. The defense budget is large, but not enough to affect everyone all at the same time. But for example, if the secretary of defense decides to close a base, that would have impact on most people in that community, if not all of them, at least indirectly. Businesses would have to adjust or close, and the military personnel and their families would have to move. And the political leadership of the community would be empowered to make decisions about the civilian use of properties previously owned by the Department of Defense.

Almost every kind of company does business with the Department of Defense, either directly or indirectly. The commissaries stock food and medicine and all sorts of regular items that the military buys, in addition to equipment for fighting.

And then there’s research and development. Historically, the Defense Department has put a lot of money into those efforts, which has had a lot of effect on consumers’ lives. It’s not just the internet, although that’s one example of something that was invented for military purposes and then translated into civilian use. A lot of smaller developments happen, too, because when a lot of money is being poured into innovation, they discover things along the way that can be commercialized.

Nowadays the civilian sector has outpaced the Defense Department in terms of research and development and innovation, but the defense dollars still make a big difference.

What personal or professional attributes make for an effective defense secretary?

I worked for four of them, three directly. Robert Gates had a high sense of empathy and lots of prior government experience. Leon Panetta had an acute sense of humor and a direct but funny way of interacting. He also had the advantage of having held multiple high-level jobs in other parts of the government. Chuck Hagel had a direct line to the Senate, and Ashton Carter was a hard-driven expert.

The most useful attributes include honesty, empathy, a sense of humor, a sharp intellect, the ability to learn quickly and the skill to determine what is important quickly. Of course, prior government experience working with the department is invaluable. It’s helpful to have an understanding of how the Defense Department works, with all its components, and its strengths and weaknesses, before you get into the job. The department has a military and civilian bureaucracy, and it takes some savvy work to get it to move quickly to implement the president’s strategy.

During the confirmation process, like all nominees, the secretary is required to attest in writing and sometimes verbally that they will provide truthful answers to Congress and that they will be responsive when Congress has questions.

Different secretaries do a better job at that than others. Secretary Donald Rumsfeld often would annoy members of Congress because he knew there was a time limit on his ability to speak and on each senator’s ability to speak. So he would just speak until the clock ran out, and that made them mad. He wouldn’t always answer questions directly and sometimes came off as arrogant.

The interactions with Congress are this delicate dance, because a secretary wants to protect the prerogatives of the president and the executive branch. But Congress pays the bills, provides any new authorities the secretary might be seeking and can curtail both the authority and the budget. A secretary wants to defend the policies, the budget and the actions of the Department of Defense. But they also want to be respectful of Congress’ role and responsibilities and the individual members of Congress.

Sometimes that balance is hard to strike. They’re in a really demanding job, and they get called to testify in front of Congress, usually with the TV cameras on. Members of Congress aren’t always polite, so it takes a lot of patience and self control on the part of the secretary of defense to successfully maintain good relations, public and private, with members of Congress.

What do the American people deserve from a defense secretary?

The secretary should be someone who will stand up for the military and civilians in the department and demand from the president and Congress the resources needed to execute their mission and to provide for the well-being of the personnel, who are, after all, Americans.

I would also say a secretary should interact with the media in a way that strikes the right balance between informing the American public about what the department and the military are doing in the name of the American people and protecting national security secrets. At the end of the day, the secretary of defense is working for the American people in their interest and that of the nation.

This story is part of a series of profiles of Cabinet and high-level administration positions.The Conversation

Evelyn Farkas, Executive Director, McCain Institute, Arizona State University

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