Download Lecture 10

force
mass
acceleration
Independent variables ?
Dependent variables ?
How does object’s motion
depends on the applied force and
the mass of the object
http://phet.colorado.edu/simulations/si
ms.php?sim=Forces_in_1_Dimension
 
a  Fnet
 1
a
m

 Fnet
a
m


Fnet  0  a  0
Newton’s First Law!
The acceleration of the object is
directly proportional to the net force.
The acceleration of the object is
inversely proportional to the mass.
Newton’s Second Law
Units!
Check the limiting cases!
A manikin exerts a constant horizontal
force on a large box. As a result, the
box moves across a horizontal floor at a
constant speed v0.
The constant horizontal force applied
by the manikin:
(A) has the same magnitude as the
weight of the box.
(B) is greater than the weight of the box.
(C) has the same magnitude as the total
force which resists the motion of the
box
(D) is greater than the total force which
resists the motion of the box
(E) is greater than either the weight of
the box or the total force which resists
the motion of the box.
A hockey puck slids with a
constant speed in a straight
line from point “a" to point “b"
along a frictionless horizontal
surface. When the puck
reaches point “b", it receives
an swift horizontal "kick" in the
direction of the heavy print
arrow, perpendicular to the
original sliding motion.
Which of the paths below
would the puck most
closely follow after
receiving the kick?
b
a
kick
A
C
B
D
E
a
b
kick
Along the frictionless path the
puck takes, the speed of the
puck after receiving the kick:
A. is constant.
B. continuously increases.
C. continuously decreases.
D. increases for a while and
decreases thereafter.
E. is constant for a while and
decreases thereafter.
Homework
Section 4.1, 4.2, 4.3
(don’t read
“The Gravitational Force”)
Problems (p.111)
#2, 6, 10, 12
Quiz
Draw a motion diagram and
force diagram for a ball thrown
into the air for four different time
intervals:
a) The ball is in your hand as
you’re throwing it upwards.
b) The ball has left your hand
and traveling upwards to the top
of its trajectory.
c) The ball is traveling
downwards from the top of its
trajectory to the point just before
you catch it.
d) The ball is in contact with
your hand as you catch it and it
comes to a stop.