Forces can be pushes or pulls and are measured in Newtons. A net force is the combination of all forces acting on an object. An unbalanced net force will cause a change in an object's motion, while a balanced net force will not. Friction and air resistance are types of forces that oppose motion. Gravity is an attractive force between objects that depends on their masses and distance between them. Newton's second law relates force, mass, and acceleration.

1. Forces

2. ForceForce 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 ObjectsA force is always exerted by an object and always acts on another object.

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

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

6. ForceForces come in pairsForces have a magnitude and a directionMagnitude: 5NDirection: north (up)5N, north (up)

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

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

9. Balanced ForcesBalanced forces do not cause change in motionThey are equal in size and opposite in direction

10. Unbalanced ForcesWhen 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 Forces3 N, right – 6 N, left = 3N, left

12. Unbalanced Forces4 N, left – 10 N, right =6N, right

13. Newton’s Second Law of MotionForce = mass X accelerationF = maForce 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.