# Recognizing Forces

The purpose of this activity is to utilize an understanding of the various types of forces in order to analyze a given situation and to identify the presence (or absence) of a variety of forces.

There are several situations described below. For each situation, decide which forces are present and absent; identify what features of the situation you used to determine the presence (P) or absence (A) of each force. Then use the "pop-up menus" to view the answers.

1. A block hangs at rest from the ceiling by a piece of rope. Consider the forces acting on the block.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

2. A block hangs from the ceiling by a spring. Consider the forces acting on the block when it is at rest (at its equilibrium position).

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

3. A ball is shot into the air with a spring-loaded cannon. Consider the forces acting on the ball while it is in the air.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

4. A skydiver (who hasn't opened his parachute yet) falls at terminal velocity. Consider the forces acting on the skydiver.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

5. A block rests on top of a table. Consider only the forces acting upon the block.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

6. A block slides across the top of a table. Consider only the forces acting upon the block.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

7. A block rests on an incline plane without sliding. Consider the forces acting on the block.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

8. A block slides across the top of a table. Consider only the forces acting on the table.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

9. The wheels of a car are locked as it skids to a stop while moving across a level highway.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

10. A car is attached by a cable to a moving truck and is being pulled along a level highway. Consider only the forces acting on the car.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?

11. A person is sitting on a sled and gliding across loosely-packed snow along a horizontal surface. Consider only the forces acting on the person.

Gravity: P or A?
Spring: P or A?
Tension: P or A?
Normal: P or A?
Friction: P or A?
Air Resistance: P or A?