The study of the interactions between matter and energy Physics The study of the interactions between matter and energy

Isaac Newton England 1642 – 1727

Isaac Newton 3 Laws of Motion optics – light and lenses gravity motion of the planets calculus physics 3 Laws of Motion

Newton’s First Law of Motion (the Law of Inertia) An object at rest will remain at rest FOREVER unless some force acts upon it An object in motion will remain in motion in a straight line FOREVER unless some force acts upon it

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

We stopped pulling, the books stopped. WHY? Was Newton WRONG? We stopped pulling, the books stopped. WHY? Maybe Newton was wrong about force and motion Or… maybe some force was changing the motion of the books!

There are NOT as many forces as you might think Different forces There are NOT as many forces as you might think gravitational All atoms attracted to all other atoms atomic P+, n0 and e- over VERY short distances mechanical Matter touching matter electromagnetic Opposites attract and likes repel

When analyzing forces, we draw arrows called VECTORS An arrow works perfectly because a force can only act in one direction VECTORS show us the direction and magnitude (strength) of the forces

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

There is NO SUCH THING as a perfectly smooth surface. What causes Friction? There is NO SUCH THING as a perfectly smooth surface. Under a microscope we see that atoms and molecules stick out and make bumps and grooves on every surface

Walnut Leaf shown through an electron microscope

Glass under an electron microscope

Wherever matter touches matter there will be friction. When two surfaces try to move across each other, the bumps and grooves get caught on each other THAT’S FRICTION! Wherever matter touches matter there will be friction.

Uses of friction Friction allows us to CONTROL motion When moving objects, friction makes it harder to move them. Friction turns work energy into HEAT

Friction turns work energy into HEAT Uses of friction http://www.youtube.com/watch?v=3wAjpMP5eyo http://www.youtube.com/watch?v=TGAnWgvl7SE&feature=related Friction turns work energy into HEAT http://www.youtube.com/watch?v=fHW9CgLMiqw&feature=related http://www.youtube.com/watch?v=-zV2I9NAEyQ

Wherever matter touches matter, there will be friction AND HEAT. Controlling Friction Wherever matter touches matter, there will be friction AND HEAT. It can NEVER truly be eliminated, but there are some things that can change the friction

Keep the surfaces from touching Controlling Friction Smooth Surface Make the bumps smaller Lubricant Fill in the grooves, put a layer between surfaces The bumps and grooves roll across instead of getting snagged Wheels or rollers Keep the surfaces from touching Use air, magnetism or magic

Do forces always change motion? What happens here?

Do forces always change motion? What happens here?

Net force – the force that is left after all the forces are calculated If the net force is 0, there is no change in motion!

10N 10N

10N 4N

5N 10N 5N 5N 10N 3N

What happens to the speed of this cart?