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# Demonstrate How Earth's Rotation Affects Launching a Rocket into Space

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Author: Janice VanCleave

### What You Need to Know

Rotation is the spinning of an object about its axis, which is an imaginary line through the center of the object. Velocity is the speed of an object in a certain direction. Escape velocity is how fast an object must travel to escape the pull of gravity (the force that pulls things toward the center of the Earth) in order to be launched into space.

### How Does Escape Velocity Work

When you throw a ball up it falls back to Earth. This is because gravity causes the ball to continue to slow until it stops its upward movement, then it starts falling back to Earth. If you throw the ball harder, it starts off with a greater velocity and will go higher before gravity causes it to stop. How hard would you have to throw a ball to prevent it from falling back to Earth? The answer is that the ball must be thrown hard enough so that its velocity is great enough that gravity cannot bring it to a stop. This starting velocity is called escape velocity.

### What Does This Have to Do with the Effect of Earth's Rotation on Launching Rockets?

You are sitting in a convertible and throw a ball out the window. The ball is thrown with a force so that the velocity of the ball is 20 miles (32 km) per hour. However, if the car is moving at 50 miles (80 km) per hour north and you throw the same ball with the same force, the velocity of the ball will depend on the direction you throw it. If it is thrown in the same direction the car is moving, the ball's velocity will be the sum of the velocity of the car and the velocity of the ball, which is 70 miles (112 km) per hour north. But if the ball is thrown in the opposite direction from the one the car is moving, the ball's velocity will be the difference between the velocity of the car and the ball, which is 30 miles (48 km) per hour north. Because the car is going faster than the ball is being thrown, the ball will still be traveling in the same direction as the car, only slower. Earth's rotation has the same effect on the speed and direction of rockets launched from its surface.

### Fun Fact

Contrary to popular belief, Earth's rotation does not cause water draining from sinks and bathtubs to spin differently in the Northern and Southern Hemispheres. Instead, the water spins in a direction determined by several factors, such as the shape of the sink or the tub and the way in which the water is moving before the drain is opened.

### Real-Life Science Challenge

One of the biggest challenges of space travel is for spacecrafts to achieve escape velocity. It takes an enormous amount of fuel for the spacecraft to move fast enough to break away from Earth's gravitational pull. The fuel adds weight to the spacecraft, and when an object is heavier, it takes more energy to lift it. To create more energy, you need more fuel. Scientists are working on ideas for lighter vehicles, more efficient fuels, and new methods for producing the needed energy to achieve escape velocity.

### Experiment

Now, start designing ways to demonstrate how rotation affects launching a rocket.

Hints

• You could use a merry-go-round to represent the rotating Earth and a small beanbag to represent a rocket.
• Design a way to launch the beanbag.
• Measure how far the beanbag travels when it is launched in the direction of rotation and when it is launched in the opposite direction.