Introduction to Forces

6. The average force required to move ____ is 3 N in the experiment on page 154.
8. The force that resists motion.
10. When there is no change in a surface, the normal force is ___ to the force applied by an object.
11. Contact forces require contact between the agent and an object, e.g. a ___ hitting a ball (pg 152).
12. Answer to question 1(a) on page 152.
13. the natural tendency of an object to resist changes in motion.
14. These have size and direction.
16. The force that a surface exerts on an object resting upon it.
18. Jet planes experience ____ friction as they move through the air.

1. Forces are measured in this unit.
2. Newton's 1st law is often referred to as this.
3. Without friction, there would be no stopping a moving object and no ___ (page 154).
4. Newton's ___ ___ states that an object at rest stays at rest, and an object in motion stays in motion.
5. Answer to question 5(f) on page 153.
7. The normal force is always ____ to the surface.
9. Which would produce lower friction to slide a box on, ice or sandpaper?
11. A ___ force has a net force equal to zero Newtons.
15. For a rolling ball to stop, a force must be applied in the ________ direction.
17. Forces can change an object's ____.