Draw a diagram of a rocket taking off and use labelled arrows to represent the forces acting on the rocket.
Forces: Moving Faster and Slower
Learning Intentions
In this topic we are learning to: z Compare balanced and unbalanced forces. z Discuss useful and nuisance friction effects. z Explore streamlining in nature and technology.
In Fig. 17.4.1, the dog and person are both tugging on the toy with equal force. Because of this, they do not move, as the forces cancel each other out. The forces are balanced.
The toy is said to be in equilibrium. Equilibrium is a state of balance between opposing forces.
Pulling force of dog Pulling force of person
If the dog began to exert a greater force, he would pull the person to the left. The forces would then be unbalanced. Unbalanced forces cause objects to speed up, slow down or change direction.
Fig. 17.4.1 Balanced forces
Balanced but Moving
An object can have balanced forces acting on it when it is moving. Consider a car driving along a road.
Force due to car engine
Fig. 17.4.2 The force driving the rocket upwards is greater than the force pulling it downwards. As a result, the rocket takes off.
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Resistance from road and air
Fig. 17.4.3
The car in Fig. 17.4.3 is being driven forward by the force of the engine, while its motion is being resisted by its grip on the road and by the air.
In this case, the forces are equal but the car continues to move with a constant speed. This is known as dynamic equilibrium.
Another example of dynamic equilibrium is when a skydiver falls at a steady speed from the sky after opening their parachute.
