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# Newton's Laws

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A summary of Newton's 1st, and 2nd laws.

A summary of Newton's 1st, and 2nd laws.

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### Transcript

• 1. Chapter 4 section 1 The first law of motion
• If the net force acting on an object is zero, the object remains at rest
• Or, if the object is moving, it continues in a straight line with constant speed
• What’s another way to say “net force equals zero”?
• 2. Unbalanced Forces Change Velocity
• Skateboard at rest stays at rest until you push it.
• The velocity increases while you are pushing it-unbalanced forces
• Why does it slow down and stop?
• The unbalanced frictional force acts to slow it down- change the velocity
• 3. Inertia and Mass
• All objects have a property called inertia
• It is the tendency of an object to resist an change in its motion
• A dirt bike rider trying to take a corner as fast as he can
• The inertia of an object depends on the mass
• The greater the mass the greater the inertia
• 4. Inertia and the First Law of Motion
• The first law of motion is sometimes called the law of inertia
• What happens in a head on car crash?
• The car stops, but the passenger not wearing a seat belt continues to move forward at the same speed the car was going. In about 0.02 s the person hits the dashboard
• 5.
• Force and acceleration are related
• Throwing a ball with greater force has greater acceleration than a gently thrown ball
• And
• Mass and acceleration are related
• The greater the mass the smaller the acceleration
• Softball vs baseball
• Assume you throw with same force, the softball has less velocity and acceleration
• Acceleration depends on mass as well as net force
• 6. The Second Law Motion
• States that acceleration of an object is in the same direction as the net force on the object
• Calculated a = f /m
• Change this equation to calculate force:
• f= m/a
• 7. Quiz
• Gravity depends on the ___________ of the objects and the _____________ between them.
• Newton’s first law states that in order for an object’s velocity to change, forces must be _____________.
• What is inertia?
• What is inertia directly related to?
• 2 nd law: Acceleration depends on _________ and _____________.
• Acceleration is in the same____________ of the net force.
• What is centripetal force?
• 8. Projectile Motion
• Projectile is something that is shot through the air, ie a softball
• Forward force gives it horizontal movement
• After you let go, the velocity is constant
• But there is also vertical motion caused by gravity
• Important point: horizontal and vertical motion are independent, but together make the movement look curved
• 9. What if you…
• Pitched a baseball forward and at shoulder height and dropped one straight to the ground from the same height? Which one would get to the ground first?
• They would get there at the same time- horizontal and vertical motion are independent of each other
• 10. Centripetal Force
• The net force toward the center of a curved path
• Any force which keeps an object moving in the curved path instead of shooting off straight.
• Examples?
• The force of gravity
• Friction
• 11. This week
• Thursday: review for test
• Friday: test
• If you miss the test, the make-up will most definitely be more DIFFICULT
• If you plan on being gone tomorrow, get the review from me today b/c you will still have to take the test
• 12. Review
• A projectile is what?
• Vertical motion and horizontal motion of a projectile are ____________ of each other
• What is the net force toward the center of a curved path?
• What is another way to say that?
• Example?
• 13. 4.3 Newton’s 3 rd Law
• When one object asserts a force on another, the second object exerts a force that is equal in strength and opposite in direction
• What is another way to say that?
• For every action there is an equal and opposite reaction
• 14. Action and Reaction Forces do not cancel
• Just b/c an action produces an equal and opposite reaction, that doesn’t mean the forces balance
• The forces are acting on different objects
• 15. Momentum
• Momentum is related to how much force is needed to change an objects motion
• Momentum= mass multiplied by velocity
• M = mv
• Another way to say this would be?
• The greater the mass and/or velocity, the greater the momentum
• 16. Law of Conservation of Momentum
• The momentum of an object doesn’t change unless its mass and/or velocity change
• Momentum can be transferred from one object to another
• Pool ball example