Forces and Motion

Motion and Force are governed by three laws

Called Newton’s Laws of Motion

Sir Isaac NewtonThe unit “force”, is named after himResearched gravity in the 1600’s He believed that every object in the universe

was pulling on every objectThis theory is called Newton’s Law of

Universal Gravitation.- Newton said in this theory that gravity depends on the mass of the object and the distance between them.

ForceBuoyancyThrustLiftDrag

Air resistance

Friction

Gravity

Balanced force

Unbalanced force

Science is a new language – the words explain what is happening. Some of the words are:

Force- any push or pull from one object to another.

- Units of force are Newton (N) and pound (lb)

- touch- push or pull on a door- magnetic force- compass needle

pulled north- buoyancy force- lifts lighter

substances out of denser substances

Newton’s 1st lawAn object at rest tends to stay at rest,

and an object in constant motion tends to stay in motion, unless acted upon by an unbalanced force. (also known as “law of inertia”

Balanced force- when forces act on an object without changing its motion.

Unbalanced force- force that causes an object to change its motion.

Demo 1

An Airplane has special names for its forces- thrust- the engines pull or push-lift- air moves around the wings then the plane rises-drag- broad, flat surfaces of the plane hit the air and pulls back on the rest of the plane. This process slows the plane down.- gravity- pulling the plane down to the ground.

What causes a dropped object to fall to the ground?- Gravity

Some gravity exists between you and the person next to you, why are you pulled toward Earth and not toward the other person? (talk in your group)- Gravity depends on mass and Earth has greater mass than a person

What is friction?- Force that keeps the surface of an object from easily moving past

the surface of another object

What things influence the amount of friction between objects?

- how rough or smooth a surface is, how hard objects are pressed together and the mass of the object

Friction Rub your hands together quicklyWhat happened?Test the friction of pushing in a chair with and without

weight Imagine the world without friction?

-without friction you would not be able to walk or move around because you would slip on everything- ex: ice on sidewalk or roads

Smooth objects have less friction than rough objects.Friction increases when surfaces are pressed together with

greater force.Friction increases with weight of an object

Imagine you are sky divingWhat slows you down? -Air Also known as air resistance

Drag forces are a result of air resistance Drag slows down objects much like friction.Without air resistance, a feather and a pencil

would fall at the same time.

Newton’s 3rd LawAll forces occur in pairs, and these two forces

are equal in strength and opposite in direction.

Better known as:For every action there is an equal and

opposite re-action

Demo 2

Newton’s 2rd LawThe unbalanced force on an object is equal to

the mass of the object multiplied by its acceleration.

FORCE= Mass x Acceleration How much force must be used to accelerate a 5kg

mass to 2 (m/s)s

5 kg x 2 (m/s)s= 10 N A bicycle rider is moving forward with a force of

200N and there is a 100N pulling back, What is the total force of the bicycle and rider?

200N – 100N= 100N*Acceleration decreases as your mass increases.

Experiment