Puck and Crate at Balance

In the picture

1. 1The puck: moving in a straight line at a steady speed
2. 2The ghost image: one of the evenly spaced positions in the trail
3. 3The upward arrow: the support force from the table
4. 4The downward arrow: the gravitational force on the crate

Examples

• A book lying still on a desk.
• A skater gliding straight at constant speed on level ice.

Quiz: Puck and Crate at Balance (Age 15)

1. 1

   If the forces on an object are balanced and the object is at rest, what happens to its motion?

   • When forces balance, an object at rest stays at rest.
   • It starts moving faster in a straight line.
   • It immediately changes direction.
2. 2

   If the forces on an object are balanced while it is already moving, what happens to its motion?

   • It keeps moving in a straight line at a constant speed.
   • It gradually slows down until it stops.
   • It keeps its speed but curves to one side.
3. 3

   What happens to an object’s motion when the forces on it cancel out?

   • The object must stop moving.
   • The motion does not change.
   • The object must speed up.

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.