Newton's Law Of Motion

1st law of Motion

The Concept of Inertia

Explain the concept of inertia

Inertia is the ability of a resting body to resist motion or a moving body to continue moving in a

straight line when abruptly stopped.

The more mass a body has, the greater its inertia and vice versa is true.

Newton's First Law of Motion

State Newton's first law of Motion

Newton’s  1st  law  of  motion  states  that

“Everybody  will  continue  in  its  state  of  rest  or  of

uniform motion unless an external force acts upon it”

Verification of Newton's First Law of Motion

Verify Newton's first law of Motion

Activity 1

Experiment

Aim:

To verif y Newton’s 1st law of motion.

Materials and apparatus:

Glass, manila card and small coin.

Procedures.

A small coin is placed on a manila card and the card is positioned on top of the glass such that

the coin is directly positioned over the open mouth of the bottle.

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Flick the card at C. Make sure that the card is not tilted by moving the finger in the horizontal

plane.

Observation:

When the  card  is flicked  away  quickly by  finger,  the  coin  drops neatly  into the

glass. The coin dropped  into  the  glass because there was no force applied on it when the card

was flipped.

Conclusion:

The coin continued  to be  at rest as the card  was  flicked quickly. This  experiment

verify Newton’s 1st law of motion.

2nd law of Motion

The Concept of Linear Momentum

Explain concept of linear momentum

Linear momentum of a body is the product of mass and velocity of that body.

Momentum = Mass, m x Velocity, v

Hence P = mv

The SI Unit of Linear Momentum

State the SI unit of linear momentum

The unit of momentum is kilogram meter per second(kgm/s)

Linear Momentum

Determine linear momentum

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When two bodies, a heavy one and the light one are acted upon by an external force at the same

time(collide) the light body builds up a higher  velocity than the heavy one  but the momentum

they gain remain the same in both cases.

i.e  Momentum  before  collision  =  Momentum  after  collision.  This  is  what  we  call  the

conservation of momentum and is described by Newton’s 2nd law of motion.

Newton's Second Law of Motion

State Newton's second law of Motion

Newton’s 2nd law of motion states that

“The rate  of change of momentum is proportional to

the applied force and it takes place in the direction of a force”

Consider  a body  of  mass, (m)  acted by  an external force (f)  from an  initial velocity (u) to the

final velocity (v) within a time interval (t).

Change of momentum = mv – mu

Hence the Newton’s 2nd law of motion can be summarized as;

“The  force  is  directly  proportional  to  acceleration of  the  object  and  the  acceleration  of  the

same body is inversely proportional to its mass”

F a ma

F = kma but k = 1

Hence F = ma

If a mass of 1kg is accelerated with an acceleration of 1m/sÇ then the force of 1N is said to be

acting on it.

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Newton

is  the force  which  when acting  on a body of  mass 1kg  it  produces an acceleration  of

1m/s..

Verification of Newton's Second Law of Motion

Verify Newton's second law of Motion

A trolley experiences  an  acceleration when  an  external force is  applied to it.  The  aim  of this

datalogging experiment is explore the relationship between the magnitudes of the external force

and the resulting acceleration.

Apparatus and materials

Light gate, interface and computer

Dynamics trolley

Pulley and string

Slotted masses, 400 g

Mass, 1 g

Clamp

Ruler

Double segment black card (see diagram)

Take care when masses fall to the floor. Use a box or tray lined with bubble  wrap  (or similar)

under heavy objects being lifted. This will prevent toes or fingers from being in the danger zone.

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Procedure

a.

Select the falling mass to be 100 g. Pull the trolley back so that the mass is raised to just

below the pulley. Position the light gate so that it will detect the motion of the trolley soon after

it  has  started  moving.Set  the  software  to  record  data,  then  release  the  trolley.  Observe  the

measurement for the acceleration of the trolley.

b.

Repeat  this  measurement  from  the same  starting  position  for  the trolley  several  times.

Enter from the keyboard '1'( 1 newton) in the force column of thetable.

c.

Transfer 100 g from  the  trolley to the slotted  mass, to increase it  to 200 g. Release the

trolley from the same starting point as before. Repeat this several times. Enter '2' (2 newtons) in

the force column of the table.

d.

Repeat the above procedure for slotted masses of 300 g and 400 g.

Conservation of linear Momentum

Difference between Elastic and Inelastic Collisions

Distinguish between Elastic and Inelastic Collisions

Elastic collision

This is the type of collision whereby each body moves with a separate velocity after collision. In

this type of collision both energy and momentum are conserved.

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Inelastic collision

Is  the  type  of  collision  whereby  all  bodies move  with  the  same  velocity  after  collision.  This

velocity is known  as common  velocity.  In  this  type  of collision energy is  not conserved, only

momentum is conserved.

Impulse

is the change of momentum which is given asm the product of force and the time taken

to change momentum.

F = mv – mu –Ft is the impulse of a force which is given by mv – mu.

The Principle of Conservation of Linear Momentum

State the principle of conservation of linear Momentum

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“When two or more bodies acts upon

Principle of conservation of linear momentum states that,

one another; that is when they collide their total momentum remains constant, provided that

there is no external force acting”

Momentum before collision = Momentum after collision

1

2

1

2

Consider  two  bodies  of  masses  m

and  m

moving  with  initial  velocities  u

and  u

and  then

move with final velocities v

1

and v

2

respectively after they collide one another.

From  the  principle  of  conservation  of  momentum:  Momentum  before  collision  =  Momentum

after collision

1

1

2

2

1

1

2

2

m

u

+ m

u

= m

v

+ m

v

The Principle of Conservation of Linear Momentum in Solving Problems

Apply the principle of conservation of linear momentum in solving problems

Activity 2

Apply the principle of conservation of linear momentum in solving problems

3rd law of Motion

Difference between Action and Reaction Forces

Distinguish between Action and Reaction Forces

Consider a book of mass, m which is at rest on  a table. This book will exert on a table with a

force equal to its weight. The table exert an equal upward force.

The downward force exerted by the book(weight) on the table is known as action force while the

upward force exerted by the table on the book is known as reaction force.

These two forces acts in opposite direction but they are equal in magnitude.

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Where; R = reaction, mg=weight of a book

Newton's Third Law of Motion

State Newton's third Law of Motion

Newton’s 3rdlaw of motionstates that

“To every action there is an equal and opposite reaction”

Application of Newton's Third Law of Motion

Apply Newton's third Law of Motion

The person firing a gun will feel the recoil when the bullet leaves the gun.

Consider a gun of mass mg ejects a bullet of mass mb with a velocity vb and the gun recoils with

velocity vg.

From the principle of conservation of momentum:

Recoil momentum of gun = Momentum of bullet

mgvg =m v