Newton’s Laws

Newton’s First Law- Inertia

Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.  What this means is that objects in motion tend to stay in motion, and objects at rest tend to stay at rest.  This property in any object is called inertia.  Also, the more mass an object has, the more inertia it has.

“Compelled to change state”

Why do objects in motion stop moving?

If any force acts upon an object, it will affect the movement.  If the force is in the opposite direction to the movement, the object will slow.  Friction is a force that, on earth, is always affecting an object. 

Force: any push or pull

Friction: the force that acts between materials that touch as they move past each other.  Caused by irregularities in the surfaces of the touching objects.  Even the smoothest objects have some friction.

Newton’s Second Law- F=ma

The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction of the net force, and is inversely proportional to the mass of the object.  This means that Acceleration equals the net force divided by the mass.  A simple way to put it is that the more mass an object has, the more force will have to be applied to get the same amount of acceleration.  Imagine hitting a baseball as hard as you can.  It will go far.  However, if you hit a bowling ball just as hard, it will not go nearly as far.

Newton’s Third Law- Two Actions

For ever action, there is an equal and opposite reaction.  This means that all actions happen in pairs. This is a fairly simple idea.  It means that whenever something hits anything else, both objects will be affected.  We all know how we can push backwards on a person with roller skates, and both people go rolling backwards.  This is a simple example of Newton’s Third Law.

Ex. Action: Ball hits bat  Reaction: Bat hits ball

Various Related Notes

Net force: a combination of all the forces acting on an object.  With no net force, objects will not change their state of motion.

Normal force is an upward force that balances the weight of an object.  This is also called support force.  Without normal force, we would all be crushed into the center of the Earth.

Equilibrium occurs when the net force is zero.

Tension is another force that often acts upon objects.  If an object is at equilibrium, the tension equals weight.

Applying force: Pressure.

Pressure is the force per unit area, measured in pascals. Pascals equal Newtons over meters squared.

Newtons: = kg*m/s (mass times acceleration)  Newton’s are simply a unit of force.