There Are Three Basic Laws of Motion

Newton’s Laws

There are three basic laws of motion:

Newton’s First Law: An object will remain at rest or moving at a constant velocity unless it is acted upon by an unbalanced force.

Inertia is the tendency of an object to resist a change in motion. Ex. When you are riding your bike fast, you have the inertia to keep moving forward even when you put on the brakes.

The greater the mass, the greater the inertia.

Newton’s Second Law: Acceleration depends on the net force acting on the object and on the object’s mass.

When an unbalanced force acts on an object, the object will accelerate in the direction of the unbalanced force.

Ex. When you pedal a bike you are creating an unbalanced force that moves the bike forward.

acceleration = force/mass or force = mass X acceleration

The unit of force is the newton (N) and is the force needed to move a 1kg object 1m/s2.

Example: How much force will be needed to give an acceleration of 1.2 m/s2 to an object that has a mass of 750 kg?

F=ma

F=(750kg)(1.2m/s/s)

F = 900 kgm/s/s or N

Newton’s Third Law: If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. Or for every action there is an equal and opposite reaction.

Ex. When you pedal a bike in the hardest gear, the pedal’s force back on your foot is the same as your foot’s force on the pedal.

Momentum is a product of the mass X velocity of an object.

What is the momentum of a wave if its mass is 670 kg and its velocity is 238 m/s?

M=mv

= (670 kg)(238 m/s)

= 160,000kgm/s

The Law of Conservation of Momentum states that the total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects.

2m/s 0m/s .5m/s 1.5m/s

  collision  

Before the collision After the collision

Calculate the momentum of each square before and after the collision. Each square has a mass of .4kg.

White square before: .4kg(2m/s)=.8kgm/s

Black square before: .4kg(0m/s)=0kgm/s

White square after: .4kg(.5m/s)=.2kgm/s

Blacksquareafter: .4kg(1.5m/s)=.6kgm/s

Total momentum before: .8kgm/s + 0kgm/s=.8kgm/s

Total momentum after: .2kgm/s + .6kgm/s=.8kgm/s

A satellite is any object that orbits another object in space.

Ex. The moon is a satellite of Earth.

Centripetal Force is a force that causes an object to move in a circular path. It is a force directed inward and is perpendicular to the object’s direction.

Newton’s First Law:

Newton’s Second Law:

Newton’s Third Law: