expt. 4 friction

8/3/2019 Expt. 4 Friction

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Experiment 4

Friction


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The Concepts of Force and Mass

A forceis a push or a pull.

Contact forcesarise from physical

contact .

Action-at-a-distance forcesdo not

require contact and include gravityand electrical forces.


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Newtons First Law of Motion

Newtons First Law

0F


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Inertiais the natural tendency of anobject to remain at rest in motion at

a constant speed along a straight line.

The massof an object is a quantitativemeasure of inertia.

SI Unit of Mass:kilogram (kg)

Newtons First Law of Motion


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Newtons Second Law of Motion

Newtons Second Law

m

Fa

aF

m


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SI Unit for Force

22 smkg

smkg

This combination of units is called a newton(N).

Newtons Second Law of Motion


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Newtons Third Law of Motion


AonBBonA FF


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AonBBonA FF


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Suppose that the magnitude of the force is 36 N. If the massof the spacecraft is 11,000 kg and the mass of the astronautis 92 kg, what are the accelerations?



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.astronautOn the

.spacecraftOn the

PF

PF

2sm0033.0sa

2sm39.0Aa



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Definition of Weight

The weight of an object on or above the earth is thegravitational force that the earth exerts on the object.

The weight always acts downwards, toward the centerof the earth.

On or above another astronomical body, the weight is thegravitational force exerted on the object by that body.

SI Unit of Weight:newton (N)

The Gravitational Force


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Relation Between Mass and Weight

mgW


2sm80.9gOn the earths surface:


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Relation Between Mass and Weight



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The Normal Force

Definition of the Normal Force

The normal force is one component of the force that a surfaceexerts on an object with which it is in contact namely, thecomponent that is perpendicularto the surface.


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N26NF

N4NF

The Normal Force


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Static and Kinetic Frictional Forces

When an object is in contact with a surface there is a forceacting on that object. The component of this force that is

parallel to the surface is called thefrictional force.


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When the two surfaces are

not sliding across one anotherthe friction is calledstatic friction.



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The magnitude of the static frictional force can have any value

from zero up to a maximum value.

MAX

ss ff

Ns

MAX

s Ff

10 s is called the coefficient of static friction.



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Note that the magnitude of the frictional force does

not depend on the contact area of the surfaces.



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Static friction opposes the impendingrelative motion betweentwo objects.

Kinetic friction opposes the relative sliding motion motions thatactually does occur.

Nkk Ff

10 s is called the coefficient of kinetic friction.



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The sled comes to a halt because the kinetic frictional forceopposes its motion and causes the sled to slow down.


F i i


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Friction

Activity 1: Friction and Area of Contact

Area fsmax fk

1

2

3

F i ti


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Normal Force fsmax fk s k

Friction

Activity 2: Friction and Normal Force

Weight of block = _________ N.

Wooden block

Pull

Mass

Du

al-Range

ForceS

ensor

F i ti


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Friction

Activity 3: Friction and nature of Surfaces in Contact

Surfaces in Contact fsmax fk


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Activity 4: Effect of lubricant

F i ti


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Friction

Activity 5: Air Resistance (Physics with Computers)

Number of Filters Terminal Velocity (Terminal Velocity)2

Motion

Detector

Interface


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expt. 4 friction

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