Download Motion

Motion
• A change in the position of an object
• Caused by force (a push or pull)
Force
•
•
•
•
A push or pull on an object
Measured in units called newtons (N)
Measured with a spring scale
Forces act in pairs
Types of Force:
–
–
–
–
–
–
Gravity
Electric
Magnetic
Friction
Centripetal
Normal
Balanced Forces
• When all the forces acting on an object are equal (net
force is zero)
• Balanced forces do not cause a change in motion.
• Balanced forces can change the physical properties of
an object without changing its motion.
• In your notes, describe an example of a balanced force.
How Can Balanced Forces Affect
Objects?
• Cause the shape of an object to change without
changing its motion
• Cause an object at rest to stay at rest or an object in
motion to stay in motion (inertia)
• Cause an object moving at a constant speed to
continue at a constant speed
• In your notes, describe an example of a balanced force
affecting an object.
Inertia
• An object at rest will remain at rest until acted upon
by an unbalanced force.
• An object in motion will remain in motion until acted
upon by an unbalanced force.
• When all forces acting on an object are equal
(balanced)
Unbalanced Forces
• When all the forces acting on an object are not equal
• The forces can be in the same direction or in opposite
directions.
• Unbalanced forces cause a change in motion.
• In your notes, describe an example of an unbalanced
force.
How Can Unbalanced Forces Affect
Objects?
• Acceleration is caused by unbalanced forces:
–
–
–
–
–
–
slow down
speed up
stop
start
change direction
change shape
• In your notes, describe an example of an unbalanced force
affecting an object.
Net Force
• The total of all forces acting on an object:
– Forces in the same direction are added.
• The object will move in the direction of the force.
– Forces in opposite directions are subtracted.
• An object will move in the direction of the greater
force.
Calculating Net Force
10 N
30 N
http://commons.wikimedia.org/wiki/File:Jack-in-the-box.jpg
A child was playing with a jack in the box. The lid pushed down
with 10 N of force, while the spring pushed up with 30 N of force.
What is the net force applied by the spring?
Check Your Answer
10 N
30 N
http://commons.wikimedia.org/wiki/File:Jack-in-the-box.jpg
A child was playing with a jack in the box. The lid pushed down
with 10 N of force, while the spring pushed up with 30 N of force.
What is the net force applied by the spring?
30 N up - 10 N down = 20 N up
Calculating Net Force
30 N
Tug of War
Game
50 N
Two competitors are playing tug of war.
What is the net force? Which direction will the rope accelerate?
Check Your Answer
Tug of War
Game
30 N
50 N
Two competitors are playing tug of war.
What is the net force? Which direction will the rope accelerate?
50 N to the right – 30 N to the left = 20 N to the right
Thursday Warm up
November 13, 2014
• Draw the box and label the forces.
50N
50N
Copy the sentences and fill in the blanks.
1. The forces are ______________.
2. The net force is _____________.
3. The object will accelerate ______________.
Force and Motion Video
Visual vocabulary
Force and Motion
Force
PUSH
Motion
Speed
Velocity
&
Acceleration
Balanced Forces
Unbalanced Forces
Friday Warm up
November 14, 2014
• Find the formula for Force on your formula chart
and write it down.
• Calculate the force (N) of an object if the mass is
25kg and the acceleration is 2.3 m/s².
Objects affected by unbalanced forces
move like…
Objects affected by balanced forces
move like…
Mass and Weight
• Mass is the amount of stuff (matter) in an object.
– The mass of an object will remain the same anywhere in the universe.
– Mass is measured in grams or kilograms.
• Weight is the mass (kg) of an object multiplied by the
acceleration of gravity (9.8 m/s2).
– The weight of an object depends on the gravitational pull of the
location in the universe.
– The gravitational pull on the Moon is only 1/6 of Earth’s gravitational
pull.
– Weight is measured in newtons (N).
Mass and Weight
Example: F=ma
A person with a mass of 25 kg x 9.8 m/s2 gravitational
acceleration is equal to 245 N of weight force.
F= 25 kg x 9.8 m/s2
F = 245 N
The person exerts 245 N of force on the ground.
If the person went to the Moon, they would only weigh 1/6
of 245 N.
Force
Force (N) = mass (kg) x acceleration (m/s2)
F
÷
m
x
a
Force
Acceleration (m/s2) = force (N) ÷ mass (kg)
F
÷
m
x
a
Force
Mass (kg) = force (N) ÷ acceleration (m/s2)
F
÷
m
x
a
Practice
The acceleration of a sprinter is 10 m/s2. The force exerted
on the starting blocks is 650 N. What is the mass of the
sprinter?
Force =
Mass =
Acceleration =
Check Your Answer
The acceleration of a sprinter is 10 m/s2. The force exerted
on the starting blocks is 650 N. What is the mass of the
sprinter?
Force = 650 N
Mass = 65 kg
Acceleration = 10 m/s2
Mass = force ÷ acceleration
Mass = 650 ÷ 10
Mass = 65
Practice
A 56 kg cart is accelerating at 15 m/s2. Calculate the force
exerted on the cart?
Force =
Mass =
Acceleration =
Check Your Answer
A 56 kg cart is accelerating at 15 m/s2. Calculate the force
exerted on the cart?
Force = 840 N
Mass = 56 kg
Acceleration = 15 m/s2
Force (N) = mass (kg) x acceleration (m/s2)
Force = 56 x 15
Force = 840
Practice
A boat is pulling a 54 kg wake boarder. The force causing the
acceleration is 108N. Calculate the acceleration of the wake
boarder.
Force =
Mass =
Acceleration =
Check Your Answer
A boat is pulling a 54 kg wake boarder. The force causing the
acceleration is 108N. Calculate the acceleration of the wake
boarder.
Force = 108 N
Mass = 54 kg
Acceleration = 2 m/s2