1. Forces and Motion
Unit F
Ch. 1

2. What are forces? A force is a push or a pull.
It causes objects to accelerate which means to speed up, slow down, stop, or change direction
A force is equal to the mass of a moving object times its acceleration.
For every force there is an equal and opposite reaction force.

3. Newton’s Second Law of Motion
Force = mass X acceleration
The greater the force, the greater the acceleration.
The greater the mass of an object the less the acceleration if the same force is applied.

4. What is friction? Friction is a force which opposes motion.
Friction is an important force in our lives. We rely on friction in many ways. An athlete usually wears shoes which provide him or her with a greater friction between the shoe and the surface. We rely on friction as an important aspect of our motion. In what other ways does friction play a role in our everyday lives?

5. From Glencoe Physical Science

6. What causes friction?
There are two factors which affect friction between two surfaces:
Kind of surfaces in contact (rough or smooth)
Amount of force pressing the surfaces together.
The rougher the surface and the stronger the force between the surfaces, the greater the amount of friction.

7. Magnetism
Magnetism is the force of repulsion or attraction between poles of a magnet
Opposite poles attract
Same poles repel

8. What is Gravity? Gravity is a force of attraction between two objects.
Law of Gravitation – any two masses exert an attractive force on each other. The amount of attraction depends upon two things: the mass of the objects and the distance between the objects.

9. Gravity causes weight
The weight of an object is caused by the force of attraction between the earth and objects on the surface of the earth.
Gravitation force is equal to weight, therefore…

10. What is weight?
When an astronaut moves away from the earth they “lose” weight. Weight is caused by the force of attraction between the earth and objects on its surface. The greater the distance an object has from the earth, the less the force of attraction which would exist.

11. What is projectile motion?

12. Balanced Forces Forces always work in pairs
Balanced forces are equal size and opposite in direction
They cancel each other out

13. Unbalanced Forces
Occur when one force is greater than its opposite force
Motion CHANGES: speeds up, slows down, stops, or changes direction
This is called Acceleration

14. Net Force
Adding or subtracting the individual forces gives a value, called a Net Force, of the combined forces
ONLY for unbalanced forces
Same direction: add
Opposite direction: subtract
Direction of the net force acts in the same as the larger force

15. Work and Effort
Work is the use of force to MOVE an object through distance
If effort is applied but nothing moves there is no work being done
Work is measured in Joules
Work= force (N) x distance (m)

16. Power Power is the amount of work done for each unit of time
It is a measure of how quickly someone or something does work
Watt is the unit of power
Power(W)= Work(J)/Time(sec)

17. Machines Simples machines make work easier
Pulley, wheel and axle, screw, inclined plane, lever, wedge
Compound machines like a shovel or faucet are made of 2 or more simple machines