The faster you drive, the greater the impact or striking power of your vehicle. The laws of physics determine that the force of impact increases with the square of the increase in speed. So, if you double the speed of a car, you increase its force of impact four times.

Inertia. Sometimes this first law of motion is referred to as the law of inertia. Inertia is the property of a body to remain at rest or to remain in motion with constant velocity. Some objects have more inertia than others because the inertia of an object is equivalent to its mass.

As we increase the force on an object the acceleration increases proportionally. Since the mass does not change as the acceleration increases, we can say that force is equal to acceleration. Force is directly proportional to acceleration (force ~ acceleration) As force increases acceleration increases.

If two objects have the same mass and a greater force is applied to one of the objects, the object which receives the greater force will change speeds more quickly. For example if a ball is hit harder, it will speed up faster.

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

No object is at rest in all frames of references. For example: Relative to the ground I’m at rest, but relative to a car I’m in motion. An objects spin or velocity can be at rest while the other is not, as is the case for the moon.

Force can make things move, change shape or change their speed. Some forces are direct and happen when two things touch (like a foot kicking a ball) or over a distance (such as a magnet or gravity). Friction is the force between two objects in contact with each other that will resist an attempt to move them.

Positive or negative acceleration means the velocity is changing. Yes. You have zero acceleration when the body is at rest (to the right stuff).

Finding the acceleration Thus, even though the velocity of an object at rest must be zero, acceleration can clearly be non-zero for objects at rest. A particle that is thrown vertically upwards stops momentarily at the highest point of motion.

An object which moves in the positive direction has a positive velocity. If the object is slowing down then its acceleration vector is directed in the opposite direction as its motion (in this case, a negative acceleration).