All About Forces

What is the unit of force in the metric system?

• kilograms
• celsius
• centimeters
• newtons

Which of these is evidence that an unbalanced force is acting on an object?

• The mass of the object is changing.
• The object remains at rest.
• The motion of the object is changing.
• The object continues moving in a straight line at constant velocity.

A rock is resting on top of a hill. The rock suddenly begins moving down the side of the hill. Why did the rock begin to move?

• An unbalanced force acted on the rock and caused it to move.
• A sudden change in gravitational force caused the rock to begin to move.
• Balanced forces caused the rock to move, and then gravity kept it moving. 
• An upward force balanced the gravitational force, so the rock began to move.

During a baseball game, a hitter strikes the ball with a bat. When this happens, the ball and the bat exert a force on each other. Why does the ball accelerate away from the bat more than the bat accelerates away from the ball?

• The ball has less mass, so it exerts less force on the bat.
• The ball has less mass, so the equal force on the ball and the bat causes greater acceleration on the ball.
• The ball has greater velocity before the collision, so force affects the ball more than it affects the bat.
• The bat exerts more force than the ball because the batter is exerting a force on the bat as it hits the ball.

Jessica has two balls. One ball has a mass of 1 kg. The other ball has a mass of 2 kg. She pushes each with a force of 100 N. How does the acceleration of the two balls compare?

• The 1-kg ball accelerates the same as the 2-kg ball.
• The 1-kg ball accelerates half as much as the 2-kg ball. 
• The 1-kg ball accelerates twice as much as the 2-kg ball.
• The 1-kg ball accelerates four times as much as the 2-kg ball.

What must two objects have for gravity to exist between them?

• mass
• volume
• solidness
• roundness

Your weight on the moon is about one-sixth of your weight on Earth. Why do you weigh less on the moon?

• The moon exerts a greater gravitational force because it is more dense than Earth.
• The moon exerts a smaller gravitational force because it has less mass than Earth.
• The moon exerts a greater gravitational force because it is closer to Earth than the sun. 
• The moon exerts a smaller gravitational force because objects are closer to its center than on Earth.

Which statement about the universality of gravity is false?

• Any two objects that have mass also have a force of gravity acting between them, no matter how far apart they are.
• The gravitational force between two objects depends only on their masses
• The gravitational force between two objects increases if mass is added to one object.
• The gravitational force between two objects increases if the objects move closer together. 

Imagine a weightless box floating in space. The following picture shows the forces acting on this box

• North
• East
• North East
• West

Imaging that a chair on the floor experiences two horizontal forces. One force measures 200 N and the other force measures –200 N. Which of the following statements describes what is happening to the chair?

• The chair’s motion is not changing.
• The chair's motion is changing.
• The chair is moving faster.
• The chair is not moving.