PhysicsPhysicsThe study of the interactions The study of the interactions between matter and energybetween matter and energy

Isaac Newton

England 1642 – 1727

Isaac Newtonoptics – light and lenses

gravity

motion of the planets

calculus

physics

3 Laws of Motion

Newton’s First Law of MotionNewton’s First Law of Motion(the Law of Inertia)(the Law of Inertia)

• An object at rest will remain at An object at rest will remain at rest FOREVER unless some rest FOREVER unless some force acts upon itforce acts upon it

• An object in motion will remain An object in motion will remain in motion in motion in a straight linein a straight line FOREVER unless some force FOREVER unless some force acts upon itacts upon it

Was Newton WRONG?Was Newton WRONG?

We pulled the books, they We pulled the books, they started moving, we let go, started moving, we let go, and just like Newton said and just like Newton said they just kept on they just kept on going……….no….wait…..going……….no….wait…..

Was Newton WRONG?Was Newton WRONG?

We stopped pulling, the We stopped pulling, the books stopped. WHY?books stopped. WHY?

Maybe Newton was wrong Maybe Newton was wrong about force and motionabout force and motion

Or… maybe some force was Or… maybe some force was changing the motion of the changing the motion of the

books!books!

Different forcesDifferent forces

There are NOT as many There are NOT as many forces as you might thinkforces as you might think

• gravitational gravitational

• atomicatomic

All atoms attracted to all other atoms

P+, n0 and e- over VERY short distances

• electromagneticelectromagnetic Opposites attract and likes repel

• mechanicalmechanical Matter touching matter

When analyzing forces, we draw arrows called VECTORS

VECTORS show us the direction and magnitude (strength) of the forces

An arrow works perfectly because a force can only act in

one direction

Friction

http://www.youtube.com/watch?v=rhZCyQ3emQg

What causes Friction?What causes Friction?

There is NO SUCH THING as a There is NO SUCH THING as a perfectly smooth surface.perfectly smooth surface.

Under a microscope we see Under a microscope we see that atoms and molecules stick that atoms and molecules stick

out and make bumps and out and make bumps and grooves on grooves on every every surfacesurface

Walnut Leaf shown through an electron microscope

Glass under an electron microscope

When two surfaces try to move across each When two surfaces try to move across each other, the bumps and grooves get caught other, the bumps and grooves get caught

on each otheron each other

THAT’S FRICTION!THAT’S FRICTION!

Wherever matter touches matter there will be friction.

Uses of friction

When moving objects, friction When moving objects, friction makes it harder to move them.makes it harder to move them.Friction turns work energy into Friction turns work energy into

HEATHEAT

Friction allows us to Friction allows us to CONTROL motionCONTROL motion

Uses of friction

Friction turns work energy into Friction turns work energy into HEATHEAT

http://www.youtube.com/watch?v=fHW9CgLMiqw&feature=related

http://www.youtube.com/watch?v=-zV2I9NAEyQ

http://www.youtube.com/watch?v=TGAnWgvl7SE&feature=related

http://www.youtube.com/watch?v=3wAjpMP5eyo

Controlling FrictionControlling Friction

Wherever matter touches Wherever matter touches matter, there will be frictionmatter, there will be friction

AND HEATAND HEAT..

It can It can NEVERNEVER truly be truly be eliminated, but there are some eliminated, but there are some

things that can change the things that can change the frictionfriction

Controlling FrictionControlling Friction

Smooth Surface Make the bumps smaller

Lubricant Fill in the grooves, put a layer between surfaces

Wheels or rollersThe bumps and grooves roll across instead of getting snagged

Keep the surfaces from touchingUse air, magnetism or magic

Do forces always change motion?Do forces always change motion?

What happens here?What happens here?

Do forces always change motion?Do forces always change motion?

What happens here?What happens here?

Net force – the force that is left after all Net force – the force that is left after all the forces are calculatedthe forces are calculated

If the net force is 0, there is no change If the net force is 0, there is no change in motion!in motion!

10N 10N

10N10N

10N 4N

5N

5N

10N

10N3N

5N

10N

What happens to the speed of this cart?