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Chapter 6Newton’s Laws
Sir Isaac Newton
December 25, 1642 - March 20 1727
• key figure in scientific revolution
• ideas considered beginning of modern science
• described planetary motion, theory of color, law of cooling, studied speed of sound.
• Made many discoveries in Calculus
wikipedia
Newton’s First Law of MotionThe law of inertia
Newton’s first law of motion
“An object at rest will stay at rest and an object in motion will stay in motion with the same velocity unless acted on by an unbalanced force”
REPEAT IT!
Newton’s first law of motion
“An object at rest will stay at rest and an object in motion will stay in motion with the same velocity unless acted on by an unbalanced force”
WRITE IT!
Newton’s first law of motion
“An object at rest will stay at rest and an object in motion will stay in motion with the same velocity unless acted on by an unbalanced force”
tell a friend
Newton’s first law of motion
Example: Explain what that means for egg sitting in a carton. (try telling an egg to move)
Example: Explain what that means for a car moving at a constant speed.
Newton’s first law of motion
Unbalanced Force - forces that result in a net force on an object and can cause changes in motion.
REPEAT IT!
Newton’s first law of motion
Unbalanced Force - forces that result in a net force on an object and can cause changes in motion.
WRITE IT!
Newton’s first law of motion
Unbalanced Force - forces that result in a net force on an object and can cause changes in motion.
TELL A FRIEND ABOUT IT!
Newton’s first law of motion
Example: eggs spinning.
- Prediction: What should happen if I spin the egg on this table?
Newton’s first law of motion
Example: eggs spinning.
- Prediction: Are the forces acting on the egg balanced?
- Time the length of time a hard boiled egg spins and a raw egg spins.
Newton’s first law of motion
Inertia - The property of an object that resists change in its motion.
Repeat it!
Newton’s first law of motion
Inertia - The property of an object that resists change in its motion.
WRITE IT!
Newton’s first law of motion
Inertia - The property of an object that resists change in its motion.
TELL IT TO A FRIEND
Newton’s first law of motion
Inertia - The property of an object that resists change in its motion.
- “Inertia is a property of matter.” <- where have you heard that before?
Newton’s first law of motion
Inertia:
Example: Stopping a spinning raw egg vs stopping a spinning boiled egg.
What is the unbalanced force acting on the egg?
Newton’s first law of motion
Inertia:
Example: What will if we pull a card out from underneath a coin?
Why?
Draw a free body diagram for the coin.
Newton’s first law of motion
Inertia:
Example: What will happen if we push the car with goofy standing on it?
Why?
Draw a free body diagram for the goof.
Newton’s first law of motion
Inertia:
Example: What will happen if we push the car with goofy standing on it, with a “seat” to hold him in place, and the object crashes into a wall?
Why?
Draw a free body diagram for the goof.
Newton’s first law of motion
Inertia:
Example: In light of goofy’s crash why is it important that you wear a seatbelt?
Newton’s first law of motion
Why is a stack of many books harder to push than a single book?
Newton’s first law of motion
Why is a stack of many books harder to push than a single book?
- YES FRICTION! but is that it?
Newton’s first law of motion
Imagine trying to push a bowling ball compared to pushing a soccer ball. The soccer ball will be easier to move.
Just because of friction?
Newton’s first law of motion
Imagine trying to punt a bowling ball compared to punting a soccer ball. The soccer ball will be easier to punt.
That has nothing to do with friction.
Newton’s first law of motion
INERTIA depends on MASS
- the larger the mass, the harder it is to change an objects motion.
Newton’s first law of motion
INERTIA depends on MASS
- the larger the mass, the harder it is to change an objects motion.
Repeat it!
Newton’s first law of motion
INERTIA depends on MASS
- the larger the mass, the harder it is to change an objects motion.
WRITE IT!
Newton’s first law of motion
INERTIA depends on MASS
- the larger the mass, the harder it is to change an objects motion.
Tell it to a friend.
Newton’s Second Law of MotionForce = mass x acceleration
NEWTON’S SECOND LAW
Second law states:
Acceleration is Force divided by Mass
REPEAT IT!
NEWTON’S SECOND LAW
Second law states:
Acceleration is Force divided by Mass
WRITE IT!
NEWTON’S SECOND LAW
Three main Ideas:
1. Acceleration is the result of unbalanced forces (ie. if there’s a net force there is acceleration)
2. A larger force makes a proportionally larger acceleration.
3. Acceleration is inversely proportional to mass.
NEWTON’S SECOND LAW
Three main Ideas:
2. A larger force makes a proportionally larger acceleration.
compare a rocket powered car to a go cart.
NEWTON’S SECOND LAW
Three main Ideas:
3. Acceleration is inversely proportional to mass.
Explain why your shopping cart will go slower and be harder to push if it contains one hundred 1 kg books, compared to one containing a single 1 kg book.
Explain why I’m okay with heading a soccer ball but not a medicine ball.
Newton’s third Law of Motion
action/reaction
Newton’s Third Law
For every action force there is reaction force that is equal in strength and opposite in direction.
Newton’s Third Law
What would happen if I jumped up and landed on the earth. Did I put more force on the earth or did the earth place more force on me?
momentum - the mass of an object times its velocity
P = m*v
conservation of momentum - as long as interacting objects are not influenced by outside forces, the total amount of momentum is conserved.
conservation of momentum - as long as interacting objects are not influenced by outside forces, the total amount of momentum is conserved.
http://www.youtube.com/watch?v=denlqdQv6OA
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