Transcript Forces and Motion

Forces and Motion
• Forces can create changes in
motion (acceleration)
• Deceleration is negative
acceleration
Motion can be described as
• a change in an
object’s position
• Average velocity
(speed) is the change
of position of an
object over time
Velocity Graphs
V = distance
time
• Velocity (v) is the
slope (rise over
run) of a position
(d) vs. time (t)
graph
Distance (m)
Velocity
60
40
Series1
20
Series2
0
1 3 5 7 9 11 13 15
Time (sec)
40 The diagram represents the total travel of a
teacher on a Saturday. Which part of the trip is
made at the greatest average speed?
FQ
How do we work this one?
GR
Calculate v = d/t for each segment.
HS
J T
Acceleration Graphs
Acceleration
Velocity ((m/s)(m)
• Acceleration (a) is the
slope of a velocity (v)
vs. time (t) graph
• Plotted on a distance
vs. time graph,
acceleration is an
exponential curve
60
40
20
0
1
3
5
7
9
Time (sec)
11
13
15
Acceleration is a change in an objects
velocity (speed or direction)
• When an object’s
speed changes over
time it is accelerating
(or decelerating)
• A = vfinal – vinitial
time
• Units for acceleration
m/s/s or m/s2
Definition of a Force
• A Force is a
push or a pull
Balanced Force
• A force that
produces no
change in an
object’s motion
because it is
balanced by an
equal, opposite
force.
4 The picture shows the position of a ball
every 0.25 second on a photogram. Using a
ruler, determine the velocity of the ball.
F 3.5 cm/s
G 10.5 cm/s
H 14.0 cm/s
J 28.0 cm/s
Use the ruler on the side of the chart and the
equation for velocity. The answer was H.
Measure from the center of ball 1 to the
center of ball 2 and multiply by 4.
Unbalanced
Forces
Are forces
that results
in an
object’s
motion
being
changed.
+
Friction
A force that acts in a
direction opposite to the
motion of two surfaces in
contact with each other.
Friction
Friction causes an
object to slow
down and stop.
Since the amount of
energy stays
constant, the
energy becomes
heat.
Universal Law of Gravitation
All objects in
the universe
attract each
other by the
force of
gravity
Universal Law of
Gravitation
1) the mass of the object
doing the pulling, and
Gravity varies depending on
two factors:
2) the distance from the center
of that object
On Earth gravity = 9.8 m/s/s
• For every second
that an object
falls its speed
increases by 9.8
m/s
Weight= Mass (m) X gravity (g)
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Weight Unit of mass = kg
Unit of acceleration = m/s/s
Unit of weight = Newton
1 Newton= about ¼ pound