... force is that force which only affects the speed of an object and not the direction. Friction is the force that happens when two things rub together. The effect of friction is usually to slow you down. With less friction, you can move more easily and as there is an increased amount of friction with higher masses of sand it makes it more difficult for the margarine tub to move forwards and the energy is used and wasted when being transferred from potential to kinetic to heat energy. When the tub is moving it has (translational) kinetic energy and when it stops this kinetic energy is dissipated as heat. The amount of stored energy in the elastic band is transferred to the tub as friction and the greater the mass the more energy needed to move the tub and therefore it will not travel as far. Energy is defined as ...

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