AMY SHANTA BABOOLALAMY SHANTA BABOOLAL

PHYSICS PROJECT:PHYSICS PROJECT:

MECHANICSMECHANICS

ARISTOTLE’S ARGUMENTSARISTOTLE’S ARGUMENTS

• One of his well known arguments is: to One of his well known arguments is: to understand change, a distinction must be made understand change, a distinction must be made between the form and matter of a living thing. For between the form and matter of a living thing. For example a sculpture has the form of a human but example a sculpture has the form of a human but the matter of bronze. If the bronze is molded into the matter of bronze. If the bronze is molded into a new form, then a change has just occurred.a new form, then a change has just occurred.

• He also thought of movement as a type of He also thought of movement as a type of change, by observing what occurs when change, by observing what occurs when something is created or destroyed.something is created or destroyed.

NEWTON’S THREE LAWS OF NEWTON’S THREE LAWS OF MOTIONMOTION

• FIRST LAW: States that an object at rest tends to stay FIRST LAW: States that an object at rest tends to stay at rest and an object in motion continues to move at rest and an object in motion continues to move with the same velocity, unless the object is acted with the same velocity, unless the object is acted upon by an unbalanced force. Inertia is the property upon by an unbalanced force. Inertia is the property which causes this change in motion.which causes this change in motion.

• SECOND LAW: When a force acts on a body the rate SECOND LAW: When a force acts on a body the rate of change of momentum is proportional to the of change of momentum is proportional to the applied force and takes place in the direction which applied force and takes place in the direction which the force acts, giving the equation: the force acts, giving the equation: F = maF = ma

• THIRD LAW: The statement used to describe this law THIRD LAW: The statement used to describe this law is: For every action there is an equal and opposite is: For every action there is an equal and opposite reaction.reaction.

WHAT IS A FORCE?WHAT IS A FORCE?

A force can be simply described as a push A force can be simply described as a push or a pull that causes a change in the state or a pull that causes a change in the state of motion of and object. When a force is of motion of and object. When a force is applied to an object it may cause the applied to an object it may cause the object to change in:object to change in: shape,shape, sizesize oror motionmotion. .

Forces are represented using arrows and Forces are represented using arrows and can be either contact or non – contact.can be either contact or non – contact.

The unit for force is Newton.The unit for force is Newton.

DYNAMICAL SYSTEMSDYNAMICAL SYSTEMS When a an object is at rest, it takes a force to get it moving. Likewise, when When a an object is at rest, it takes a force to get it moving. Likewise, when

an object is moving it takes a force to stop. an object is moving it takes a force to stop. To explain Newton's first law, we can use the example of the X and brakes in To explain Newton's first law, we can use the example of the X and brakes in

a car. For the car to move from rest, a force has to be applied to the X a car. For the car to move from rest, a force has to be applied to the X similarly, for the car to stop a force has to be applied to the brakes.similarly, for the car to stop a force has to be applied to the brakes.

In Newton’s second law, we see that multiplying the acceleration and mass of In Newton’s second law, we see that multiplying the acceleration and mass of an object, we can get the force needed to move the object. For example to an object, we can get the force needed to move the object. For example to move a roller coaster with mass 4500kg moving at an acceleration of move a roller coaster with mass 4500kg moving at an acceleration of 1000ms1000ms-1-1, the force needed is 4500kg*1000ms, the force needed is 4500kg*1000ms-1-1 = 4500000N = 4500000N

When we walk, we exert a force on the ground, and the ground exerts an When we walk, we exert a force on the ground, and the ground exerts an equal but opposite force on our foot, causing it to come back up. This proves equal but opposite force on our foot, causing it to come back up. This proves Newton’s third law; each action has an equal and opposite reaction.Newton’s third law; each action has an equal and opposite reaction.

WHAT IS LINEAR MOMENTUM?WHAT IS LINEAR MOMENTUM?

• Momentum is the physical quantity that takes into account both the mass and velocity of an object.

• It can be associated with Newton’s first and second laws.

• The linear mass of an object can be described as the mass of the object multiplied by its velocity i.e. p=mv

• It is measured in kgms-1.

LINEAR MOMENTUMLINEAR MOMENTUM

• An example used to demonstrate linear momentum is: A ball A of mass 5kg is traveling north at 6ms-1. Another ball B of mass 3kg is traveling south at 4ms-1. To find the momentum of each, we multiply the mass by the velocity. The momentum of ball A was found to be 30kgms-1 and the momentum of ball B was found to be 12kgms-1.

THE LAW OF CONSERVATION OF THE LAW OF CONSERVATION OF LINEAR MOMENTUM.LINEAR MOMENTUM.

The statement used to describe The statement used to describe the law of conservation of linear the law of conservation of linear momentum is: Provided that the momentum is: Provided that the vector sum of the external vector sum of the external forces acting on a system is forces acting on a system is zero, the total linear momentum zero, the total linear momentum of that system remains constant of that system remains constant during collisions.during collisions.

Momentum can be conserved Momentum can be conserved for all interactions in which the for all interactions in which the vector acting on the force is vector acting on the force is zero.zero.

When we use collisions, we see When we use collisions, we see that the momentum before and that the momentum before and after a collision are equal.after a collision are equal.

After collisions, one of the following may After collisions, one of the following may occur:occur:

Both objects come to a complete stopBoth objects come to a complete stop Both objects move together in the Both objects move together in the

same direction.same direction. Both move off in the opposite Both move off in the opposite

direction.direction.

EXAMPLE: Two trains are on the same EXAMPLE: Two trains are on the same track. Train B of 200kg is stationary track. Train B of 200kg is stationary and train A is moving at 80ms-1 with and train A is moving at 80ms-1 with mass 150kg. If they collide train A mass 150kg. If they collide train A pushes train be off to a spade 30mspushes train be off to a spade 30ms-1. -1.

What is the speed of train A?What is the speed of train A?

MM11UU11 + M + M22UU22=M=M11VV11 + M + M22VV22

(150*80) + (200*0)=(150*V(150*80) + (200*0)=(150*V11) + (200*30) ) + (200*30)

12000 = 150V12000 = 150V11 + 6000 + 6000

12000 -6000 = 150V12000 -6000 = 150V11

6000/150 = V6000/150 = V11

VV11 = 40 MS = 40 MS-1-1

CIRCULAR MOTION AND FORCES

• A force is needed when an object is moving in circular motion.

• The force keeps the object in place.• Without the force, the object may move out of

orbit. • The force provides attraction between the two

objects present.• If a force is not present there will not be an

attraction between the objects.

CIRCULAR MOTION AND FORCESCIRCULAR MOTION AND FORCES When an object moves in uniform circular motion, it means that the When an object moves in uniform circular motion, it means that the

object moves in a circle with constant speed, but not constant object moves in a circle with constant speed, but not constant velocity. The velocity is not constant because the direction is velocity. The velocity is not constant because the direction is continuously changing.continuously changing.

When an object, in circular motion is accelerated towards the centre When an object, in circular motion is accelerated towards the centre of the circle a of the circle a centripetal forcecentripetal force causes the acceleration and changes causes the acceleration and changes the direction without changing the speed.the direction without changing the speed.

The formula for finding the centripetal force in a circle is: The formula for finding the centripetal force in a circle is: FFcc = =

mvmv22/r/r, where r is the radius of the circle., where r is the radius of the circle. EXAMPLE 1:When the Earth orbits the Sun, an unbalanced force, EXAMPLE 1:When the Earth orbits the Sun, an unbalanced force,

gravity, is present. This gravitational force of attraction between the gravity, is present. This gravitational force of attraction between the Earth and the Sun, provides the centripetal force needed for circular Earth and the Sun, provides the centripetal force needed for circular motion.motion.

EXAMPLE 2: When a car is going around a bend, the frictional EXAMPLE 2: When a car is going around a bend, the frictional force acting on the tires of the car provides the centripetal force force acting on the tires of the car provides the centripetal force needed.needed.