Balanced and unbalanced forces
'Unchanging motion' is when the body is A stationary object which has a speed of zero. For example, the bus started from rest before it reached a speed of 8 m s-1. or is moving with a steady speed in a straight line. When the total force in opposite directions are equal in magnitude. For example, with a thrust of 15 N and a frictional force of 15 N, the body experiences balanced forces. are responsible for unchanging motion.
Balanced forces are forces where the effect of one force is cancelled out by another. A tug of war, where each team is pulling equally on the rope, is an example of balanced forces. The forces exerted on the rope are equal in size and opposite in direction. The rope will have an acceleration of zero under the action of these balanced forces. It will therefore remain Not moving..
Example
Question
A cyclist travelling at \(10\, m\,s^{-1}\) has a forward force of \(200 N\) but is acted on by friction and A force of friction produced when an object moves through the air. of \(200 N\) which push against her.
What happens to the cyclist's motion?
The forces are balanced, cancelling each other out, so there is NO CHANGE in the cyclist's motion – the cyclist continues at a When the speed of body does not change, eg the car was travelling at a constant speed of 30 m s-1. of \(10\, m\,s^{-1}\).
Balanced and unbalanced forces
'Changing motion' includes movement where the body is speeding up or slowing down. It also includes motion where the direction in which the body moves is changing, ie the body is moving in a curved path. It is When the force in one direction is more than the force in the opposite direction. Eg: With a thrust of 20 N and an opposing frictional force of 15 N, the object experienced an unbalanced force of 5 N in the direction of the 20 N force. Sometimes called the 'resultant force' or 'net force'. that cause 'changing motion'.
The lift-off of a space rocket is an example of an unbalanced force in action. The space rocket accelerates upwards from its launch pad. The A force used to move a body forwards or up, eg the rocket had a thrust of 10,000 N. (\(T\)) from the A rocket is usually a chemically fueled vehicle that exerts a large force while burning a small volume of fuel. Generally used to launch objects high into the atmosphere or into space. Eg: the rocket launch allowed the satellite to be put into orbit. engines is greater than the The force acting on an object due to the pull of gravity from a massive object like a planet. The force acts towards the centre of the planet and is measured in newtons (N). (\(W\)) of the rocket system. Because force \(T\) is greater than the force \(W\), the effect of one force does not cancel that of the other. The forces acting are unbalanced.
