MANIPAL Newtons Laws of Motion

7/30/2019 MANIPAL Newtons Laws of Motion

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Newtons

Laws of Motion

I. Law of InertiaII. F=ma

III. Action-Reaction


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Newtons Laws of Motion

1st Law An object at rest will stay atrest, and an object in motion will stay inmotion at constant velocity, unless actedupon by an unbalanced force.

2nd Law Force equals mass timesacceleration.

3 rd Law For every action there is anequal and opposite reaction.


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1st Law of Motion

(Law of Inertia)

An object at rest will stay at rest, and an object in motionwill stay in motion at constant velocity, unless acted upon by an unbalanced force.


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1st Law

Unless actedupon by an

unbalancedforce, this golf ball would sit onthe tee forever.


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1st Law

Once airborne,unless acted onby anunbalanced force(gravity and air fluid friction),it would neverstop!


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1st Law

Inertia is thetendency of an

object to resist changes in itsvelocity:whether inmotion ormotionless.

These pumpkins will not move unless acted onby an unbalanced force.


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Why then, do we observe everyday objects in motion slowingdown and becoming motionlessseemingly without an outside

force? Its a force we sometimes cannot see

friction.


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There are three types of friction:Static friction: initial friction when moving an object

Sliding friction: ice skatingFluid friction (air or liquid): air or water resistance

What is this unbalanced force that acts on an object in motion?


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Slide a book across a table and watch it slide to a restposition. The book comes to a rest because of the presence of a force -that force being theforce of friction - which brings the book to a rest position.


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In the absence of a force of friction, the book would continue in motion with the same speedand direction - forever! (Or at least to the endof the table top.)


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Newtonss 1 st Law and You

Dont let this be you. Wear seat belts.

Because of inertia, objects (including you) resist changesin their motion. When the car going 80 km/hour is stoppedby the brick wall, your body keeps moving at 80 m/hour.


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2nd Law

The net force of an object isequal to the product of its massand acceleration, or F=ma.


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2nd Law

When mass is in kilograms and acceleration isin m/s/s, the unit of force is in newtons (N).One newton is equal to the force required toaccelerate one kilogram of mass at onemeter/second/second.


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2nd Law


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2nd Law (F = m x a)

How much force is needed to accelerate a 1400kilogram car 2 meters per second/per second?Write the formulaF = m x aFill in given numbers and unitsF = 1400 kg x 2 meters per second/secondSolve for the unknown

2800 kg-meters/second/second or 2800 N


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Newtons 2 nd Law proves that different massesaccelerate to the earth at the same rate, but withdifferent forces.

We know that objects with different massesaccelerate to theground at the samerate.

However, because of the 2 nd Law we know

that they dont hit theground with the sameforce.

F = ma

98 N = 10 kg x 9.8 m/s/s

F = ma

9.8 N = 1 kg x 9.8 m/s/s


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3rd Law

For every action, there is anequal and opposite reaction.


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3rd Law

According to Newton,whenever objects A andB interact with each

other, they exert forcesupon each other. Whenyou sit in your chair,your body exerts a

downward force on thechair and the chairexerts an upward forceon your body.


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3rd Law

There are two forcesresulting from thisinteraction - a force on

the chair and a force onyour body. These twoforces are called action and reaction forces.


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Newtons 3rd Law in Nature

Consider the propulsion of afish through the water. Afish uses its fins to pushwater backwards. In turn,the water reacts by pushingthe fish forwards, propellingthe fish through the water.The size of the force on the

water equals the size of the

force on the fish; thedirection of the force on thewater (backwards) isopposite the direction of theforce on the fish (forwards).


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3rd Law

Flying gracefullythrough the air, birdsdepend on Newtonsthird law of motion. Asthe birds push down onthe air with their wings,the air pushes their

wings up and givesthem lift.


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Consider the flying motion of birds. A bird flies byuse of its wings. The wings of a bird push airdownwards. In turn, the air reacts by pushing the birdupwards.The size of the force on the air equals the size of theforce on the bird; the direction of the force on the air(downwards) is opposite the direction of the force onthe bird (upwards).Action-reaction force pairs make it possible for birdsto fly.


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MANIPAL Newtons Laws of Motion