1. Motion and Energy
Forces and Motion

2. force,push,pull
A __________ is any ________ or _______ from one object to another.

3. newton,pound
2. Units of force are the ___________ (N) and the ___________ (lb.) When we draw diagrams of forces, we often use arrows to show the direction and the strength of a force.

4. spring scale
3. A _________ _________ is a tool used to measure force. The spring stretches as it pulls on an object, and the pointer show the force of the pull.

5. magnetic
4. Many forces occur as one object touches another, such as the pull of a tow truck on a broken down car. Other forces, though, may act on an object without objects touching. An example would be a compass because is uses the ___________ force of Earth.

6. thrust,lift,drag
5. An airplane has special names for its forces. The engine pulls or pushes the plane forward, this is called _________. As the plane moves forward, air moves around the wings and raises the plane into the air: This is called ________. The force pulling back on the plane, slowing it down is called _________.

7. gravity
6. The force that pulls all objects together is called __________.

8. increases,decreases
7. Newton said that gravity depends on the masses of the objects and the distance between them. Increasing the mass ____________ the force, and increasing the distance ____________ the force.

9. Friction
8. _________ is a force that opposes the motion of one object moving past another.

10. surfaces
9. Friction depends on two factors: the ___________ of two objects and how hard the objects are pushed together.

11. less friction
10. Smooth surfaces usually have ________ ___________ than rough surfaces.

12. Heat
11. _________ is created whenever there is friction.

13. air resistance
12. Drag forces are a a result of ___________ _______________. Broad, flat surfaces have the most drag.

14. balanced forces, opposite
13. When forces act on an object without changing its motion, they are called ____________ __________. Balanced forces often point in ___________ directions. There may be more than one pair of balanced forces acting on object. The forces on stationary objects are always balanced.

15. unbalanced force
14. A force that causes an object to change its motion is called an ______________ __________.

16. forced
15. Newton´s first law states that objects do not change their motion unless __________ to do so.

17. increases,decreases
16. According to Newton´s second law, an object´s acceleration __________ as the amount of unbalanced forces on it increases.; an object´s acceleration _________ as the object´s mass increases.

18. force
17. When one object pushes on a second object, the second object pushes back on the first object with the same amount of __________, or strength.

19. action force, reaction force
18. The push of the first object is called the ________ _______. The push on the second object back on the first is called the ________ _________.