# Force and motlon

## Force

Force We now wish to define the unit of force. We know that a force can cause the acceleration of a body. Thus, we shall define the unit of force in terms of the acceleration that a force gives to a standard reference body. As the standard body, we shall use (or rather imagine that we use) the …

## Newton’s First Law

Newton’s First Law Before Newton formulated his mechanics, it was thought that some influence, a force was needed to keep a body moving at constant velocity. Similarly a body was thought to be in its natural state when it was at rest. For it to move with constant velocity, it seemingly had to be propelled in some way …

## What Causes an Acceleration

What Causes an Acceleration If you see the velocity of a particle-like body change in either magnitude or direction, you know that something must have caused that change (that acceleration). Indeed, out of common experience, you know that the change in velocity must be due to an interaction between the body and something in its surroundings. For example, …

## Force and motion

Force and motion On April 4, 1974, John Massis of Belgium managed to move two passenger cars belonging to New York’s Long stand Railroad. He did so by clamping his teeth down on a bit that was attached to the cars with a rope an . then leaning backward while pressing his feet against the rail  ties. The cars together weighed about 80 …