Newton S Laws of Motion
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Notes: Newton’s First Law of Motion
“During the years 1665 and 1666, Isaac Newton developed three laws that describe all of the states of motion—rest, constant motion, and accelerated motion. In addition, these three laws explain how forces cause all of the states of motion.” (Prentice Hall Science)
The Role of Friction
. Imagine a hockey puck is sliding across a very large sheet of ice. It eventually slows
to a stop.
o Why does the hockey puck eventually stop? ______
o What would happen to the hockey puck if there was no ______?
. Newton realized that friction causes objects to act differently than they would without it.
. He recognized that if friction were not present:
o an object in motion would continue to move forever
o an object at rest would stay at rest unless it was acted upon by an unbalanced
force.
Standard(s): 1.4 TA: ______Independence Level: ______% Assistance, coaching, prompting: ______. Example: a football lying on a field would not fly off by itself.
. Review: Balanced and Unbalanced Forces
o The forces acting on an object can be combined.
o The total force is often called the ______force.
o When two forces point in the same direction, you ______the forces
together to get the total force.
o When two forces point in opposite directions, you ______the forces
to get the total force.
. The net force acts in the direction of the ______force.
o When the total force is 0N, the forces on the object are said to be
______.
o When the total force is non-zero, the forces on the object are said to be
______.
. Inertia: the tendency of objects to remain in motion or stay at rest
o Basically, objects resist changes in motion.
o The more ______something has, the more ______it has.
o Thus, inertia is related to ______.
. Newton’s First Law of Motion: an object at rest will remain at rest and an object in
motion will remain in motion at constant velocity unless acted upon by an unbalanced
force.
o Basically, things tend to keep doing what they are already doing!
. If an object is not moving, it will stay not moving.
. If an object is moving, it will stay moving (in a straight line). o If you want to change what the object is doing, you must apply force!
. Applications of Newton’s First Law
o What happens when you are riding in a car and the car stops suddenly?
. You feel as if you are ______.
. Why do you feel as if you are ______?
o What happens when you are in a car that is stopped and it suddenly starts
moving?
. You feel as if you are ______.
. Why do you feel as if you are ______?
o What happens when you are in a car and the road turns?
. You feel as if you are ______to the ______.
. Why do you feel as if you are ______to the
______? o If an elephant were chasing you, its enormous mass would be very
threatening.
. Why?
. But if you zigzagged, the elephant’s mass would be to your advantage.
Why?
o It is more efficient to cut vegetables with a massive cleaver rather than a small
knife. Why? Explain in terms of inertia.
Newton’s Three Laws of Motion—Summary:
Newton’s 1st Law: Forces are necessary to change the motion of an object.