Forces

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.

Forces Act on Objects

• A force is always exerted by an object and always acts on another object.

Net Force

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

Net Force

• A net force acting on a stationary object will move the object.

Force

• Forces come in pairs• Forces have a magnitude and a direction

5N, north (up) Magnitude: 5NDirection: north (up)

Balanced and Unbalanced Forces

• Forces occur in pairs and they can be either balanced or unbalanced

Balanced Forces

• A stationary object will not move while the forces acting on it are balanced.

Balanced Forces

• Balanced forces do not cause change in motion

• They are equal in size and opposite in direction

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

Unbalanced Forces

3 N, right – 6 N, left = 3N, left

Unbalanced Forces

4 N, left – 10 N, right = 6N, right

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.

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?

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.

• 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.

What is Gravity?