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MOTION AND LIQUIDS

PREPARED BYV.REVATHIAMBIKALECTURER IN PHYSICS

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MOTION

• A change in the position of a body or system with respect to time, as measured by a particular frame of reference. Only relative motion can be measured; absolute motion is meaningless.

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INFERENCE

1. A body is said to be in the state of rest when it remains in the same position with respect to time.

2. A body is said to be in the state of motion, when it continuously changes its position with respect to time.

3. The distance between the two places is not the same; it depends upon the path chosen.

4. The shortest distance, or distance travelled along a straight line, is known as displacement.

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MOTION CLASSIFICATION

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Motion Classification

Uniform

• If an object covers equal distances in equal interval of time

Non-Uniform

• If an object covers unequal distances in equal interval of time

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Measuring the rate of motion

The distance travelled in one second or rate of distance travelled.

Total distance travelled

Time taken

SpeedThe distance covered when travelled along a straight line.

Total covered distance

Time taken

Displacement

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Rate of motion

Velocity Acceleration

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VELOCITY ACCELERATION

It is the displacement made in one second or rate of change of displacement.

DISPLACEMENT TIME

UNIT : meter/ second

Uniform velocity :

Equal distance covered by a body in equal intervals of time

It is the change in velocity of an object per second or rate of change of velocity. CHANGE IN VELOCITY TIME TAKEN

UNIT : meter / second2

Uniform Acceleration :

If an object travels in a straight line and its velocity increases or decreases by equal amount in equal intervals of time, then the acceleration of the object is uniform.

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GRAPHICAL EQUATION OF MOTION

1. Equation for Velocity at a time v = u + at

2. Equation for displacement s = ut + ½ at2

3. Equation for velocity at a position v2 = u2 + 2as

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Acceleration due to gravity

♣ When a the body is allowed to fall down, the velocity gradually increases. Now the body is accelerated.

♣ The deceleration or acceleration due to the gravitational force of earth is known as acceleration due to gravity.

It is denoted by “ g”The value of “ g” is 9.8 m/s 2

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Uniform circular motion

Circular motion :

An athlete runs along the circumference of a circular path or The movement of an object in a circular path

Uniform circular motion :

When an object moves in a circular path with a constant velocity.

The magnitude of the velocity is constant at all points and the direction of the velocity changes continuously.

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• Angular displacement :The angle covered by the line joining the body and the centre of the circle.It’s measured in radian

• Angular velocity :The angular displacement in one second or Rate of

change of angular displacement.Angular displacement

time taken ω = θ/ tUNIT : radian / second

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CENTRIPETAL FORCE

• The constant force that acts on the body along the radius towards the centre and perpendicular to the velocity of the body.

• F = mv2 /r• F = mrω2

• Since v = rω

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MOTION IN LIQUIDS

• When a body floats or immerses in a liquid, the pressure on the bottom surface is more than that the pressure on the top of the surface.

• Due to the difference in pressure, an upward force acts on the body.

• This upward force is called upthrust or buoyant force.

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Centre of buoyancy

• The upward force is called upthrust or buoyant force.

• The buoyant force (upthrust) acts through the centre of gravity of the displaced liquid which is known as centre of buoyancy.

• The buoyant force is equal to the weight of the liquid displaced.

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Archimedes principle

• When a body is immersed in fluid (liquid or gas) it experiences an apparent loss of weight which is equal to the weight of the fluid displaced.

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Relative density

• Density :Density of a body is defined as the mass per unit volume of the body.

MassVolume

UNIT : Kg / mRelative density :

It is defined as the ratio of density of the body to the density of water.

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Laws of flotation

• The weight of the floating body is equal to the weight of the liquid displaced by it.

• The centre of gravity of the floating body and the centre of gravity of the liquid displaced (centre of buoyancy) are in the same vertical line.

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HYDROMETERSThere are two types of hydrometers

1. The constant immersion hydrometer, in which the weight of the hydrometer is adjusted to make it sink to the same fixed mark in all liquids.

2. The variable immersion hydrometer, in which the weight of the hydrometer remains the same, but the depth to which it sinks in different liquids vary.

3. A common hydrometer used to test the purity of milk by noting its specific gravity is called a LACTOMETER.

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