13.1 Gravitational force
What is the relationship between gravitational force, the movement of objects and energy?
When we climb up a mountain slope, we often find it more difficult than going down the mountain. This is because gravitational force or gravity is helping us as we move down the mountain.
The strength of the pull of gravity between two objects depends on how far apart they are and the difference in their mass.
As gravity pulls all objects downwards, let us see hw two objects fall towards the ground.
13.2 Frictional force
What is the relationship between frictional force, the movement of objects and energy?
When an object moves over a surface, there is frictional force or friction between the surface and the object. Friction causes a moving object to slow down and stop.
The larger the mass of an object, the harder the object presses on a surface. Thus, there is more friction.
The type of surface also affects friction and movement. There is more friction between an object and a rough surface than between the same object and a smooth surface.
(a) The bigger bicycle has a larger mass than the smaller bicycle. Thus, there is more friction between the bigger bicycle and the road.
(b) There is more friction between a moving car and the normal and rough road. This allows the driver to move and stop the car safely.
(c) There is less friction between a moving car and the slippery and smooth road. This makes it difficult to stop the car safely.