A constant change of speed, slowing up or slowing down.
For an object in motion will continue to keep moving at a constant velocity unless acted on by an outside force. In real world situations, what causes an object to come to a stop is a force that will oppose the motion (friction). When objects are in contact with each other, friction will act in the direction opposite to the motion and change the motion of the moving object.
Gravity is a universal force that causes objects to be attracted to each other. When no other outside force, such as friction or air resistance, acts upon a falling object, its speed increases. An object constantly gains speed for every second it falls until it reaches a maximum speed, which differs depending upon the shape of the object and the friction with the air.
Sir Isaac Newton is credited with describing laws of gravity and motion. His three laws of motion explain objects at rest, constant motion, and acceleration due to balanced or unbalanced forces exerted on objects.
The first law describes inertia, the tendency of an object to remain in motion or stay at rest.
The second law explains the dynamics of unbalanced forces
The third law notes that for every action (force), there is an equal and opposite reaction.
People use simple and complex machines to perform “everyday” tasks, which require a force to move objects. The amount of effort saved when using machines is called mechanical advantage. Machines can make work seem to be easier by changing the size or direction of an applied force. Each machine makes work easier by providing some trade-off between the force applied and the distance over which the force is applied. Through a better understanding of forces and motion, scientists and engineers have been able to design more efficient systems related to sports, recreation, transportation and human health.