Download Force Equations

Unit 8-3 Forces
Friday, October 9th, 2015, EQ#5 Block#1
EQ: What is the difference of what mass and weight measure?
Mass measures matter, weight measures force
AA: What is a force, a weight, and mass?
Force: push, pull
Weight: how heavy the object is
Mass: amount of matter in an object
Vocab
Force: a push or pull
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Symbol F
Measured in [N]
Net Force: the addition or subtraction of multiple forces on an object
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Same direction add:
To the right 20 N
To the right 30 N
Total Force is 50 N
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Different direction subtract:
To the right 20 N
To the left 30 N
Total Force id 10 N
Newton: metric unit of force,
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Unit [N]
Mass: the amount of matter in an object. “Stuff”.
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Symbol m
Unit [Kg]
Inertia: an object’s resistance to a change in motion (acceleration)
Friction: a force of resistance between two objects that are sliding
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Symbol Ff
Unit [N]
Weight: the force of gravity acting on an object
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Symbol Fg
Unit Newton [N]
Tuesday, October 13th, 2015, EQ#5 Block#2
EQ: How do mass and weight vary from place to place in the universe and why?
Weight changes because gravity changes, but mass stays the same because it has nothing to do with
gravity.
AA: In your own words, describe the inertia of the standard movements of a shopping cart full of
heavy items like 2 L soda bottles, gallons of milk, bags of sugar, and cans of soup.
Harder to push/stop when it is heavy and difficult to change its direction.
Mass vs. Weight vs. Inertia:
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Inertia is the resistance to a change in motion
Mass is the measure of inertia
m of 10 [kg] has more inertia than m of 5 [kg]
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Force is a push or a pull
It takes a force to accelerate a mass
Therefore, the more mass an object has the more force is needed to accelerate it
Weight is the measure of the force of gravity
Weight is calculated by multiplying mass times acceleration of gravity
Wednesday, October 12th, 2015, EQ#5 Block#3
EQ: What does a net force greater than zero do to an object? What does a net force equal to zero do
to an object?
AA: If bowling on the moon (compared to Earth):
Would it be easier or harder to lift up the bowling ball? Why?
Easier to lift because it weighs less. Less gravity=weighs less
Would it be easier to harder to throw the bowling ball? Why?
The same because the inertia is the same. Mass stays the same, therefore inertia is the same.
What is a force?
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A push or a pull
Forces make objects accelerate
1 [lb] = 4.44 [N]
1 [N] = 0.225 [lbs] Example: your weight [lbs]/1 x 4.44 [N]/1 [lbs]
150 [lbs] x 4.44 [N] = 667 [N]
2,000 [N] x .225 = 450 [lbs]
What do forces do?
*Newton’s Second Law
 When the net force is greater than zero
a) If the force and the motion are in the same direction, the object will speed up
b) If the force and the motion are in opposite directions, the object will slow down
*Newton’s First Law
 When the net force is equal to zero
a) An object at rest will remain at rest
b) An object in motion will stay in motion at a constant velocity
*Newton’s Third Law
a)
b)
c)
d)
Forces come in pairs
The two forces are equal in size (50 [N] = 50 [N])
The two forces are in opposite directions (50 [N] down = 50 [N] up)
Each of the forces acts on a different object
Example using two cars crashing: 50 [N] left = 50 [N] right
 When there is more than one force:
a) If the forces are in the same direction you add them
b) If the forces are in the opposite direction you subtract them
Thursday, October 15th, 2015, EQ#5 Block#4
EQ: A net force of 50 N acts on a 10 kg box. What is the acceleration of the box?
AA: What is the net force equal to when a car is moving at constant velocity to the north? What is the
net force equal to when a car is speeding up?
The net force is zero.
Any number that is greater than zero.
Force Equations:
Fnet=ma (Net Force)
Fg=mag (Weight)
Ag=9.81 [m/s2] Down on Earth
Example: A 4 [kg] mass box is accelerated at 5 [m/s2]. What is the Net Force?
Fnet=ma
(4 kg)(5 m/s2) = 20 [N]
Example: An object weighs 100 [N]. What is it’s mass?
Fg=mag
m=Fg/ag
Fg
m=100/9.81
m=10.2 [kg]
m
ag