Transcript AP Physics C IB

AP Physics C I.B
Newton’s Laws of Motion
The “natural state” of an object
Newton’s First Law – If no force
acts on a body, the velocity of
the body does not change. That
is, there is no acceleration
Specifically, the net force is zero in
the first law.
Newton’s Second Law
An object may accelerate in one
dimension or two. ΣFx = max or
ΣFy = may
Ex. Three cases for a 0.20 kg hockey puck on a
frictionless surface. Find the horizontal acceleration
when a) F1 = 4.0 N b) F2 = 2.0 N and F3 = 1.0 N at 30.0º
below the horizontal.
Ex. Find F3 which will create an acceleration of 3.0 m/s2
in the direction shown.
Ex. Three students pull on a ring with the forces shown.
The ring doesn’t move. What is the magnitude and
direction of FB?
Weight and Mass
The normal force
Tension
Newton’s Third Law – When two
bodies interact, the forces are
always equal in magnitude but
opposite in direction. This is true
whether the objects are
stationary, moving at a constant
velocity or accelerating.
Ex. For the system of blocks shown a) draw a free body
diagram on each block b) find the acceleration of the
hanging block c) and the tension in the rope.
Ex. For the hanging block shown, find the tension in
each rope.
Ex. For the block shown find a) the tension in the rope
and b) the normal force on the block.
Ex. Apparent weight of a 72 kg person in an elevator
given by the scale reading (normal force). Find the
apparent weight when a) the elevator is at rest or
moving at a constant velocity b) accelerating upward at
3.20 m/s2 and c) accelerating downward at 3.20 m/s2.
Ex. For the blocks shown find a) the acceleration of the
blocks and b) the force on block B by block A.
Friction – the book on the table
• The book is pushed and released
• The book is pushed across the table at a
constant velocity
• Pushing a stack of books
Free body diagrams
Love-hate relationship with friction
The direction of friction
Causes of friction and a couple of
equations
Ex. In 1960, the longest recorded skid marks (290 m) on
a public road, the MI highway in England, were made by
a Jaguar. How fast was the car moving at the moment it
began skidding?
Ex. A woman uses a rope to pull a loaded sled with a
mass of 75 kg along a horizontal patch of ice at a
constant velocity. The coefficient of kinetic friction
between the sled runners and ice is 0.10 and the rope
makes an angle of 42º with the horizontal. What is the
tension in the rope?
Ex. A coin rests on a book. When the book makes an
angle of 13º with the table, the coin just begins to slip.
What is the maximum coefficient of static friction
between the coin and book?