Transcript Newton's First Law

Newton’s Laws of Motion
Newton’s First Law of Motion:
An object at rest remains at rest and an object in motion
remains in motion at constant speed and in a straight line
unless acted on by an unbalanced force.
In other
words:
Part I: Objects at Rest
-Objects at rest mean they are not moving
Ex: chair on the floor, a plane on a runway
-Objects will not start moving until a push or a pull is
exerted on them.
Ex: You tend to fall backward when your school bus
starts to move.
Part II: Objects in Motion
-An object moving at a certain velocity will continue to
move forever at the same speed and in the same direction
unless some unbalanced force acts on it.
Ex: Riding in a bumper car…..car stops, but you
continue to move forward until your seat belt
stops you.
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Friction and Newton’s First Law
Friction often prevents us from observing Newton’s First Law on
everyday objects. (meaning: we don’t see things moving forever)
Ex: You want to give your desk a push so you can see it move
forever across the floor. But when you do, it quickly comes to a
stop.
WHY?
Because an unbalanced force acted on the desk to stop its
motion. That unbalanced force is FRICTION!!!
Inertia is Related to Mass
Newton’s first law is sometimes called the law of inertia
Inertia: the tendency of all objects to resist any change in motion
Inertia is the reason objects at rest remain at rest and objects in motion
remain in motion.
Inertia is the reason you slide toward the side of a car when the
driver makes a sharp turn.
Mass Is a Measure of Inertia
An object with small mass has less inertia
An object with large mass has greater inertia
This is why it is easier to start and to change the motion of an object
with a small mass.
Which of these two cars would be easier to push and stop once it
was moving?
Matchbox car
Elvis’s pink cadillac