Transcript Force in Mechanical Systems

Newton’s Laws of
Motion
Newton’s First Law - the law
of inertia
• Inertia - an object’s resistance to a
change in motion
• It takes a force to change the speed or
direction of an object.
• Inertia is directly related to mass.
Examples of inertia:
• Which is easier to push: a loaded shopping
cart or an empty one?
• You’re riding in a car and the driver slams on
the brakes. What happens?
• Your bratty nephew runs past you for the
14th time. You stick out your foot and trip
him. What happens?
Newton’s Second Law F =m x a
• The mass of an object and the force
applied to it affect its acceleration.
• As the force on an object increases, the
acceleration increases.
• As the mass of an object increases, the
acceleration decreases.
Newton’s Third Law action / reaction forces
• For every force there is an
equal and opposite
reaction force.
• When a runner pushes
against the ground, the
ground pushes back
against the runner.
Newton’s Third Law action / reaction forces
• Action-reaction forces are not the same as
balanced forces. Action-reaction forces act
on different objects.
Balanced
forces:
Both people
are pulling
on the door.
QuickTime™ and a
decompressor
are needed to see this picture.
Action-Reaction
forces:
The diver
pushes down
on the board.
The board
pushes up on
the diver.
Identify the Newton’s law that fits each situation.
1. An athlete can throw (accelerate) a baseball faster than
. a shot put.
2. A person sitting in a boat tosses a heavy anchor in one
. direction. The boat moves in the opposite direction.
3. A car skids on an icy curve and slides off the road.
4. F = m x a represents which of Newton’s Laws?
5. Which one of Newton’s Laws allows you to keep
. jumping on a trampoline?
6. A boat moves through the water because of a rowing
motion (using oars).
.
7. When a car suddenly stops at a red light, a book lying on
. the car seat slides forward.
8. A dropped basketball hits the floor and bounces back up.
9. It takes more force to accelerate a loaded dump truck
. than it takes to accelerate a small car with one
passenger.
10. A cup of water sits motionless on a kitchen table.
.