Force and Momentum Ppt

8/3/2019 Force and Momentum Ppt

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What are Forces?

Module 3


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What are forces?

In module 2 we learned that a force is a

push or a pull.

We learned that Newtons 2nd

Law statesthat a Force is equal to the mass of a

moving object times its acceleration.

We learned that Newtons 3rd Law states

that for every force there is an equal and

opposite reaction force.


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What is friction?

Friction is a force which opposes motion.

Friction is an important force in our lives.We rely on friction in many ways. Anathlete usually wears shoes which providehim or her with a greater friction betweenthe shoe and the surface. We rely on

friction as an important aspect of ourmotion. In what other ways does frictionplay a role in our everyday lives?


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From Glencoe Physical Science


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What causes friction?

There are two factors which affect

friction between two surfaces:

Kind of surfaces in contact (rough orsmooth)

Amount of force pressing the

surfaces together.The rougher the surface and the

stronger the force between the

surfaces, the greater the amount of

friction.


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What is static friction?

From Glencoe Physical Science

If you were trying to move a box likepictured below and the box did not

move, this would be static friction.

Static friction is friction between twosurfaces which are not moving past

each other.


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What is sliding friction?

Sliding friction occurs when a force is

great enough to overcome the static

friction.

Glencoe Physical Science

What is rolling friction?

Rolling friction is the friction

which enables wheels toturn and objects to move. If

there were no friction,

turning wheels would not

enable an object to move.


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Air Resistance another type of

friction?? Air resistance is a force which opposes a

moving object. This can be easily seen

with falling objects. When a piece of paper

and a crumple piece of the same type of

paper are dropped, they fall at the same

rate.

A penny and a feather dropped in air willnot fall at the same rate, but a penny and

feather dropped in a vacuum (no air) will.


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What is terminal velocity?

Forces cause objects to accelerate (2nd

Law).

When the force of gravity on a fallingobject equals the force of the airresistance going against gravity, the forcesbalance out and the object stops

accelerating. The object will travel at a constant velocity the terminal velocity.


11/25

Gravity is a force of attraction between twoobjects.

Law of Gravitation any two masses exert an

attractive force on each other. The amount ofattraction depends upon two things: the mass of

the objects and the distance between the

objects.

What is Gravity?


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What is gravitational acceleration?

When objects fall they accelerate toward

the ground.

Using Newtons 2nd

Law we can see thisrelationship: F = ma

The force caused by gravity acts upon a

certain mass to cause it to accelerate

toward the ground at a constant rate.

Acceleration due to gravity is 9.8 m/s2


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Gravity causes weight

The weight of an object is caused by the

force of attraction between the earth and

objects on the surface of the earth.

Gravitation force is equal to weight, therefore


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How much does a person with

a mass of 70.0 kg weigh onthe earth?

Weight = mass X 9.8 m/s2

Weight = 70.0 kg X 9.8 m/s2

Weight = 686 N

Remember that 1 N = (1 kg) (1m/s2)


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What is weight? When an astronaut moves away

from the earth they lose weight.

Weight is caused by the force ofattraction between the earth and

objects on its surface. The greaterthe distance an object has from

the earth, the less the force of

attraction which would exist.


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What is the difference between

mass and weight?

Mass is the amount of matter in an object. Thisdoes not change in an object as it moves awayfrom the earth.

Weight is caused by gravity. Therefore, thegreater the distance, the less the force ofattraction. The less the distance the greater theforce of attraction.

Your weight is dependent upon the mass of theearth. If you were able to go to the planet,Jupiter, your weight would be 27 time greater,because the mass of Jupiter is 27 times

greater.


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What causes weightlessness?

Even in the space shuttle, there is a

force of attraction exerted by the

earth on the shuttle and its contents. When the space shuttle temporarily

falls toward the earth, the contents

of the space shuttle appear to beweightless, but in fact they are falling

with the space shuttle. This is called

freefall.


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What is projectile motion?


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When an object is thrown into the air, two forces and

two motions affect the movement of the object.

The object may be thrown horizontally with a certainforce, but the vertical force of gravity combines to affect

the motion.

Slow projectile - shoot a

monkey

Fast projectile - shoot a

monkey


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What is centripetal force?

centripetal means to move toward the

center.

Centripetal acceleration is the accelerationof an object toward the center of a curve

or circular path.

Centripetal force is a force toward the

center of a circle which holds the moving

object in its circular path.


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Two objects in contact with one another and

moving must use the action-reaction law.

Rocket propulsion involves the action-reactionlaw. The explosion from one end of the rocket

causes a force in that direction. This causes an

unbalanced force in the opposite directioncausing the rocket to accelerate. Video Clip!


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What is momentum?

The momentum of an object is equal to

the product of its mass and its velocity.

The unit for momentum is kg m/s


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What is the Law of

Conservation of Momentum? When object collide the momentum of oneobject is transferred to the other object.

View this video to see a demonstration ofconservation of momentum.

Notice that the soccer ball has greatermomentum since it has a larger mass. Its

momentum is transferred to the smaller ballwhich has a smaller mass and will thereforehave a larger velocity. Try this with a soccerball and a tennis ball!

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Force and Momentum Ppt