1. A FORCE acting on an object causes the object to change its SHAPE or size, to start moving, to stop moving, to accelerate or decelerate. When there’s the INTERACTION between two objects they exert a force on each other, these exerted forces are equal in size but opposite in direction. When an object has SEVERAL forces acting on it, the effects of force is same as one force acting on the object in a certain direction and this overall force is called the ‘resultant force’. The resultant force is essential to change the velocity of an object.

• If the resultant force is zero the forces on the object are balanced.
• If the resultant force acting on the object is ‘zero’ then: the object will remain stationary. In such a case the object will move at a steady speed in a straight line.
• If the resultant force acting on the object isn’t zero then: the object will either accelerate or decelerate.

2. Non-contact forces – allow remote PARTS of the environment to affect an object: Magnetic force. Electric force.