1. Forces

2. Force Force is simply a push or a pull. The Newton is the unit used to express force. When you pull a stuck door, you are applying more force to the door.

3. Forces Act on Objects A force is always exerted by an object and always acts on another object.

4. Net Force Net force is the result from combining all the force exerted on an object.

5. Net Force A net force acting on a stationary object will move the object.

6. Force Forces come in pairs Forces have a magnitude and a direction Magnitude: 5N Direction: north (up) 5N, north (up)

7. Balanced and Unbalanced Forces Forces occur in pairs and they can be either balanced or unbalanced

8. Balanced Forces A stationary object will not move while the forces acting on it are balanced.

9. Balanced Forces Balanced forces do not cause change in motion They are equal in size and opposite in direction

10. Unbalanced Forces When the net force of an object is not zero, the forces on the object are unbalanced. An unbalanced force always causes a change in motion

11. Unbalanced Forces 3 N, right – 6 N, left = 3N, left

12. Unbalanced Forces 4 N, left – 10 N, right = 6N, right

13. Newton’s Second Law of Motion Force = mass X acceleration F = ma Force and acceleration are directly proportional. The greater the force, the greater the acceleration. Mass and acceleration are inversely related. The greater the mass of an object the less the acceleration if the same force is applied.

14. 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?

15. Air Resistance – another type of friction?? Air resistance is a force which opposes a moving object. This can be easily seen with falling objects. When a piece of paper and a crumple piece of the same type of paper are dropped, they fall at the same rate. A penny and a feather dropped in air will not fall at the same rate, but a penny and feather dropped in a vacuum (no air) will.

16. 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.