Newton’s Laws of Motion

1. Sir Isaac Newton---figured out three basic laws that explain common forces and how they interact to produce motion.

2. First Law (Law of Inertia) –an object will remain at rest or move with a constant speed unless a force is applied

Ø      force—push or pull; usually more than one force is acting on an object

o       net force—sum of all the forces acting on the object

o       balanced forces - forces that are equal in size and opposite in direction

o       unbalanced forces - two or more forces acting on an object that do not cancel, and cause the object to accelerate

Ø      friction - is the force that opposes motion between two surfaces that are touching each other.

o       static friction - prevents an object from moving when force is applied

o       sliding friction - slows down a sliding object

o       rolling friction - friction between the ground and wheel which allows the wheel to roll

Ø      inertia—natural tendency of an object to resist any changes in motion (depends on mass)

o       The greater the mass of an object, the more inertia it has. When inertia becomes greater, it becomes more difficult to slow down, speed up, or change the direction of a moving object. It is also harder to make an object with greater inertia start moving if it is at rest.

o       velocity-the rate of motion (speed/direction)

o       terminal velocity- is reached when the force of gravity is balanced by air resistance. Air resistance depends on size and shape of the object.  Air resistance is the force air exerts on a moving object.  This force acts in the opposite direction to that of the object’s motion.  In the case of a falling object, air resistance pushes up as gravity pulls down.

Ø      speed-the rate of motion or rate of change in position (S = d / t  or Speed = distance/time)

Ø      distance= speed X time (d = vt)

3. Second Law (Law of Momentum) – an object acted upon by a force will accelerate in the direction of the force (Force = mass x acceleration or F = ma )  
   1. The larger the net force, the greater the acceleration.
   2. An object’s mass and acceleration are inversely related: the greater the mass, the lower the acceleration.  

Ø      acceleration- is the rate of change in velocity

Ø      weight (gravitational force) - the measure of the force of gravity on an object, usually the force between Earth and an object at its surface

Ø      momentum- a property a moving object has due to its mass and velocity.   momentum=mass x velocity  (  p=m x v   )

a.       The momentum of an object doesn’t change unless its mass, or velocity, or both, change.  Momentum can be transferred from one object to another.

4. Third Law – for every action there is an equal and opposite reaction
   1. When one object exerts a force on a second object, the second object exerts a force on the first that is equal in size and opposite in direction.
   2. The forces on the wall and the ice skater are equal in size and opposite in direction. Although there are two objects involved, each object exerts one force and experiences one force. The wall does not move because it has a lot of inertia.

            c. When the fuel burns, the engine exerts a downward force on the exhaust gases. The gases exert an equal and opposite upward force on the rocket.

d. When a swimmer pushes against the water (action), the water pushes against the swimmer (reaction). The reaction force pushes the swimmer forward.