physics the study of the interactions between matter and energy
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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
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?
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