When objects collide the momentum is conserved. The total momentum of a system will not change unless an external force acts on it. The total amount of energy in the universe is conserved. In nuclear reactions it may form or be converted to mass. The law of the conservation of energy is one of the great truths of physics.
All machines are combinations of simple machines.
A machine eases the work performed by either changing the magnitude or direction of the force exerted. The six simple machines are the lever, pulley, wheel and axle, inclined plane, wedge, and screw. Work and Power Work is defined as the product of force exerted on an object and the distance the object moves. Power is the rate of doing work. Work is done only if the object is moved.