# Forces act in pairs.

## Presentation on theme: "Forces act in pairs."— Presentation transcript:

Forces act in pairs

Force engine = thrust friction = drag

support = gravity

Horizontal forces acting on a moving car thrust( force of the engine) drag( air resistance)

Forces acting on an aeroplane lift, drag, gravity, thrust L=W and T=D when the plane is flying at a constant velocity

First Law of Motion: Balanced Forces balanced forces = no change in velocity
A stationary object will never move as long as the forces acting on it are balanced.

Resultant force gives direction of acceleration
The forces acting on an object moving at a constant velocity(steady speed) are also balanced forces. If the object starts to accelerate or decelerate then the forces will no longer be equal or balanced.

What is happening to the helicopter in each picture?

Thrust equals weight. Helicopter hovers at a constant altitude.
Weight greater than thrust. Helicopter stays on the helipad or drops in altitude. Thrust is greater than weight. Helicopter takes off and increases in altitude.