11.1 Gravity in Motion

Suppose a baseball and a marble are dropped at the same time from the same height. Which ball would land first according to Aristotle? Explain.

According to Aristotle, the baseball would drop first. He thought the rate at which an object falls depends on its mass.

Why don't astronauts hit their heads on the ceiling of the falling shuttle?

Astronauts don't hit their heads on the falling shuttle because they are in free fall just like the shuttle is.

A crumpled piece of paper hits the ground before a flat sheet of paper because

Because there is more air resistance against the flat paper

Which of the following statements describes what happened when Galileo dropped two cannonballs with different masses from the same height?

Both cannonballs reached the ground at the same time.

What is centripetal force?

Centripetal force is the unbalanced force that causes objects to move in a circular path. The word centripetal means "toward the center."

What is the meaning of the acceleration value 9.8 m/s

For every second an object falls, its downward velocity increases by 9.8 m/s.

Why is a skydiver not really in free fall? Explain your answer.

Free fall occurs when gravity is the only force acting on an object. Therefore, skydivers cannot be in free fall because there is air resistance.

How does gravity affect objects in projectile motion?

Gravity pulls objects in projectile motion down at an acceleration of 9.8 m/s to the second power, the rate for all falling objects.

If there were no air resistance, what would happen to hailstones?

Hailstorms would hit the Earth at a velocity near 350 m/s.

Is the path of a ball rolling on a flat surface an example of projectile motion? Explain your answer.

No, because this is not a curved path, and the ball is not being thrown.

Is it true that an astronaut is weightless in space? Explain your answer.

No. An astronaut has mass, and so has some gravitational force exerted on him or her. Therefore, the astronaut has some weight.

If you shoot an arrow aimed directly at the bull's-eye of your target, where will the arrow hit your target? Why?

The arrow will hit below the bull's eye because the arrow accelerates downward as it moves forward.

Why do objects fall to the ground with the same acceleration?

The force of gravity is greater on more massive objects, but those objects are harder to accelerate because they are more massive. These two effects balance each other, so the acceleration is the same on all objects.

How does the velocity of a falling object change over time?

The object falls faster and farther each second than it did the second before.

The force that opposes the motion of objects through air is called

air resistance

The motion of a body when only the force of gravity is acting on the body is called _______ ________.

free fall

What are the two components of projectile motion?

horizontal motion and vertical motion

What is the horizontal motion of an object?

motion that is parallel to the ground

What is the vertical motion of an object?

motion that is perpendicular to the ground

What do you get when you subtract the force of air resistance from the force of gravity?

net force

An orbiting shuttle follows the curve of the Earth's surface as it moves at a constant speed, and so is said to be _________ Earth.

orbiting

The curved path that an object follows when thrown near the surface of the Earth is called ___________ __________.

projectile motion

What three factors affect the amount of air resistance acting on an object?

size, shape, speed

When a falling object stops accelerating, it has reached ______________ velocity.

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