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air resistance

kick

finding force

normal

force

friction

(push in

opposite

direction)

A 60 kg. woman skydives from an airplane. As she exits the plane, what is the net force applied to her?

substitute the information you can gather from the question:

F=ma

force is a push

or a pull

F= (60 kg.) (9.8 m/s)

magnitude

+

direction

forces are vector quantities

acceleration with force and mass

tension

gravity

force is measured in Newtons (N)

multiply:

if an object is moving left,

the force is negative.

if an object is moving right,

the force is positive.

F= -588 N

F= 588 kg.m/s

magnetic

force

elastic

force

remember that the force is negative because she is falling

A 2.5 kg. rifle fires a 0.0065 kg. bullet at 1200m/s. What is the rifle's acceleration? After 0.25 seconds, what is it's velocity?

one Newton is equal to one kg.m/s

Law I

first determine the force

exerted on the bullet:

now use that force to

find the acceleration

of the rifle:

F=ma

so

a=F/m

F= (0.0065 kg.) (1200m/s2)

a= -7.8 N/2.5 kg.

objects will remain in their current state of movement until acted upon by an unbalanced force

F= 7.8 N

then negate that force to determine the force exerted on the rifle by the bullet

a= -3.12 m/s2

NEGATIVE DOES NOT INDICATE A

NEGATIVE VALUE, JUST DIRECTION.

F= -7.8 N

Law II

finally, use the acceleration of the rifle and the time given to find the rifle's velocity after 0.25 seconds:

FORCES ARE ADDED TO DETERMINE THE NET FORCE:

a= vf-vi/t so vf=at=vi

v=at

v= (-3.12m/s) (0.25s)

since the

initial velocity

is 0, ignore it.

the effects of balanced and unbalanced forces

v=-0.78 m/s

balanced force: the sum of all

the forces exerted on an object is 0

unbalanced force: the sum of all the forces being exerted on one object is either more or less than 0 N

- 10 N + 10 N = 0 N

force equals the mass times the acceleration of an object

-20 N + 10 N = -10 N

-10 N + 15 N = 5 N

unbalanced;

moving right

(positive)

unbalanced;

moving left

(negative)

if the object is still moving forward but forces are being applied, the forces are balanced.

Isaac Newton was a brilliant English scientist and mathematician in the 17th and 18th century. His research and discoveries advanced the scientific revolution. Among his accomplishments were the telescope, co-creation of calculus, and, of course, Newton's Laws of Motion.

Newton's Laws of Motion

what does this mean?

A person parachuting from an airplane

has different, changing forces acted upon them:

book pushes down -10 N

In the airplane, all forces on the

person are balanced so she does not move.

If an object pushed down on a table with -10 N of force, the table will push back with 10 N of force. Even thought the signs are opposite (negative and positive) the forces are equal; remember the negative sign just means direction.

no velocity

table pushes back up 10 N

Air Resistance

Once she falls out of the airplane, she begins

to accelerate, but the air resistance is very low.

She increases in speed because the force of

gravity overpowers the small air resistance.

Law III

negative velocity-falling but accelerating

Air resistance, a type of force, is an excellent example of how net force can affect an object.

Eventually, the air resistance grows to equal the force of gravity. This is called terminal velocity, and she is now falling at a constant speed.

the force applied from object A to object B is always equal to the force applied by object B to object A

negative velocity-falling at a constant speed

Finally, she deploys the parachute. This immediately increases the air resistance and she begins to slow.

positive velocity-falling and decelerating (two negatives)

The III law states that "every action will have an equal and opposite reaction", but while this is true the objects may show the reaction differently if the mass or acceleration seen in the II law is a certain way.

If two objects are of different masses but are accelerating at the same rate, their forces will be different. If they are of different masses, and therefore exerting different forces on each other, their acceleration will not be the same either.

Sometimes the forces are balanced but a change in motion occurs. Why?

a= 4 m/s

a= 2 m/s

If two objects are of equal mass and are accelerating at the same rate, the force they apply to each other will be equal. If two objects are of equal mass and are exerting the same amount of force on each other, their acceleration will be equal.

a= 3 m/s

how do the II and III law affect each other?

This is because the forces aren't actually balanced. Though it looks like the two forces add up, only one force is acting on each object. The "yellow" force is the only one affecting the skater; the "red" force affects the wall. Because the forces exerted on him are not balanced, the skater moves.

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