Transcript Unit 3 Test Study Guide

Unit 3
Force and Motion
Study Guide
Force and Motion
• A force is a push or pull.
• Only unbalanced forces can cause
an object to stop, start, or change
directions.
• The overall force on an object after all
the forces have been added together
is the net force. ( A non-zero net
force )
• Equal forces acting on an object in
opposite directions are balanced
forces.
Know how to calculate net force in
a force diagram
550 N
700 N
Net force = 150N
Net force = 5 N
25 N
25 N
Net force = 0 N
• Inertia is the tendency of an object to
resist its change in motion.
• Friction - A force that one surface exerts
over another when the two rub against
each other.
Newtons
• Newton- the unit of force. One Newton
equals the force required to accelerate
one kilogram of mass at one meter per
second.
• 1 N = 1 kg x 1 m/s (squared)
F=mxa
• When using the formula
• F= m x a
Force is measured in Newtons
Mass is measured in kilograms
Acceleration is measured meters/second2
Sample Problem #1
• A 52 kg water-skier is being pulled by a speedboat. The
force causes her to accelerate at 2 m/s2. Calculate the
net force.
We know:
Mass = 52 kg
Acceleration = 2 m/s2
F=mxa
F = 52 kg x 2 m/s2 (multiply numbers and units)
F = 104 kg x m/s2 (change kg. m/s2 to N)
F = 104 N
Sample Problem #2
• A water skier is being pulled by a boat with
104 N of force to accelerate a skier at 2 m/s2. What is her mass?
We know:
Force = 104 N
Acceleration = 2 m/s2
Need to calculate: Mass
M = F/A
M = 104 N
2 m/s2
M = 104 kg . m/s2
2 m/s2
(Changed Newtons to kg.m/s2)
M = 104 kg . m/s2
2 m/s2
(m/s2 cancel out and you’re left with kg)
M = 52 kg
Sample Problem # 3
• A 52Kg water skier is being pulled by a boat with 104N of force.
What is her acceleration?
We know:
Mass= 52 kg
Force = 104 N
Need to calculate: acceleration
A = F/M
A = 104 N
52 kg
M = 104 kg . m/s2
52 kg
(Changed Newtons to kg.m/s2)
M = 104 kg . m/s2
52 kg
(kg cancel out and you’re left with m/s2 )
M = 2 m/s2
Work = Force x Distance
• There is no
work don’t if
there is no
movement!!
• By making the
distance you
have to move
an object
greater, you
lessen the force
needed to move
the object.
Having a longer ramp means you have to apply less force to get an object up
the ramp.
Getting the object into the back of the truck is the job. The amount of work is
the same no matter the length of the ramp. What changes is the amount of
force needed to do the work.
Work = Force x Distance
• Work is measured in Joules – J
• Force is measured in Newtons – N
• Distance is measured in meters – m
Work Problems
Sample #1
• How much work is required to pull a sled 5
meters if you use 60 N of force.
We know: D = 5 m
F = 60 N
We need to calculate: W
W = FD
W = 60 N . 5M
W = 300 Nm
W = 300 J
Work Problems
Sample # 2
• If 300 J of work was done to pull a sled 5 meters, how
much force was applied to the sled?
We know: W = 300J
D=5m
We need to calculate: F
F= W/D
F= 300 J
5m
F= 300 Nm
5m
(Change J to Nm)
F= 300 Nm
5m
( m cancel out)
F = 60 N
Work Problems
Sample # 3
If 300 J of work was done to pull a sled 5 meters, how much
force was applied to the sled?
• We know: W = 300J
•
F = 60 N
• We need to calculate: D
• D = W/F
• D = 300 J
•
60 N
• D = 300 Nm
•
60 N
(Change J to Nm)
• D = 300 N m
•
60 N
( N cancel out)
• D=5m
Force and Motion in plants
• Turgor Pressure- is the outward pressure
that occurs in a plant cell when the
cytoplasm and vacuoles fill up with water
and the cell membrane pushes against the
cell wall.
•
Geotropism
• When a plants roots
grow down into the
soil, and the shoots
grow up toward the
surface as a response
to gravity.