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Atmospheric pressure at the sea level is equal to the pressure exerted by 0.76m of mercury column. This is standard atmospheric pressure.

Going higher altitude the atmospheric pressure decreases. So blood veins are broken and blood is oozing out.

True The pressure on a surface increases with an increase in the thrust on the surface.

False For a given thrust, pressure is less on a surface of large area.

Moment of force about a point depends on the following two factors:

(a)The magnitude of the force applied and,

(b)The distance of line of action of the force from the axis of rotation.

Newton's second Law of Motion states that The rate of change of momentum is directly proportional to the force applied in the direction of force.

For example; when acceleration is applied on a moving vehicle, the momentum of the vehicle increases and the increase is in the direction of motion because the force is being applied in the direction of motion. On the other hand, when brake is applied on the moving vehicle, the momentum of the vehicle decreases and the decrease is in the opposite direction of motion because the force is being applied in the opposite direction of motion.

The moment of a couple is equal to the product of the either force and the perpendicular distance between the line of action of both the forces. S.I unit of moment of couple is Nm.

Factors affecting the moment of force : 

1. The magnitude of the force applied 

2. The distance of line of action of the force from the axis of rotation.

PRESSURE: “The thrust on unit area of the surface is called PRESSURE.”

Pressure = Thrust / Area

S.I. unit = Nm^-2

Wood, iron rod, stone and glass are rigid bodies. 

Moment of force : “The turning effect of force acting on a body about an axis is called the moment of force.”

Types of inertia:

• inertia of rest
• inertia of motion 
• inertia of direction.

• inertia of rest
• inertia of motion 

Types of inertia:

• inertia of rest.
• inertia of motion.
• inertia of direction.

Conditions for 

(a) Translational motion : Motion of rigid body in straight line and in the direction of applied force. 

(b) Rotational motion : Rigid body should rotate about axis (or pivot). 

A single force acting on a body is an unbalanced force. It produces acceleration in the body. If two or more forces act on a body such that their resultant is not zero, the resultant is an unbalanced force responsible for accelerating the body. 

Example: When a ball lying on the ground is hit with a bat, the ball is set in motion by the applied force.

Forces at a distance : “A force which does not make a direct contact with a body, but acts through space is called force at a distance or A Non-Contact Force.” 

Three examples : 

1. Gravitational force acting on a falling body. 

2. Electrostatic force between two charged particles.

The inherent property of a body by virtue of which it cannot change its state of rest is called the inertia of rest.

Examples:

1. When we dust a carpet, the carpet moves but the dust particles in it remain at rest due to inertia and hence get separated from the carpet. Hence, the carpet becomes clean. 

2. When a bus starts suddenly, the passengers experience a backwarderk due to inertia.

The inherent property of a body by virtue of which it cannot change its direction of motion is called the inertia of direction. 

Examples:

1. While sharpening a knife, sparks fly off tangentially in the sense of motion from the grinding stone. 

2. When a vehicle moves, the mud particles sticking to its wheels fly off tangentially in the sense of motion. Hence, mudguards are fitted to vehicles.

The force which occurs due to the action of muscles is called muscular force. To apply muscular force, there should be physical contact between both the objects. For example: when a bullock pulls a cart, its muscles apply the force on the cart. This happens only if the cart is bounded to the bullock.

The inherent property of a body by virtue of which it cannot change its state of motion is called the inertia of motion. 

Examples:

1. When a fan is switched off, its blades continue to rotate for some time. Due to internal friction and friction with air, the blades of the fan stop rotating after some time. 

2. Passengers in a bus experience a forwarderk when the bus stops suddenly due to application of brakes.

When a fan is switched off, its blades continue to rotate for some time. Due to internal friction and friction with air, the blades of the fan stop rotating after some time. 

2. Passengers in a bus experience a forwarderk when the bus stops suddenly due to application of brakes.

S.I. units: N m (Newton meter)

When a force is applied to an object at rest or in motion, it changes the speed and direction of motion of the object resulting in the object coming to rest or in motion in other direction with some different speed than the initial one. Therefore, a change in the speed of the object and the direction of motion of the object is referred as change in the state of the object.

Movement of force — The turning effect of force acting on a body about an axis is called the moment of force.

Force : Force is a physical cause that changes or may tend to j change the state of rest or the state of motion of an object.

The S.I. unit of force is Newton.

(i) When a force applied on a rigid object does not change interspacing of constituent molecules and does not change dimensions and can cause motion in it.

(ii) When a force applied on a non-rigid object change interspacing between its constituent particle and cause a change in its dimensions and can produce motion in it.

(a) Pull and push both can be applied through a rigid connector. 

e.g. we can pull a table with a rigid rod. We can also a table with a push rigid rol (connector). 

(b) Non-rigid connector can not be applied to push a table i.e. a rope cannot push a table to move it from one place to other. Only pull can be applied through non-rigid connector.

Two EFFECTS OF APPLIED FORCE :

(i) It can change the state of the body.

i.e. It can stop a moving object and also a force can move a stationary object.

(ii) A force can change the shape & (and size) of an object.

A Force is that physical cause which changes(or tends or change) either the size or shape or the state of rest or motion of the body.

Is moment of force a scalar or a vector-

Vector

A force when applied on a non-rigid body changes the inter-spacing between its constituent particles and therefore causes a change in its dimensions and can also produce motion in it.

On the other hand, a force when applied on a rigid body, does not change the inter-spacing between its constituent particles and therefore it does not change the dimensions of the body but causes motion in it.

The moment of force is equal to the product of the magnitude of the force and the perpendicular distance of the line of action of force from the axis of rotation. S.I. unit of moment of force is Newton metre (Nm).

(a) A fielder on the ground stops a moving ball by applying a force with his hands.

(b) The pull exerted by horse makes a cart moves.

(c) In a cycle pump, when the piston is lowered, the air is compressed to occupy a less volume.

(d) On pressing a piece of rubber, its shape changes.

(a) When the body is free to move it produces translational motion.

(b) When the body is pivoted at a point, it produces rotational motion.

Newton's first law of motion: A body continues to be in its state of rest or of uniform motion in a straight line unless an external force is applied on it. It is called the law of inertia because it tells that every material body has a property by virtue of which it resists the change in its state of rest or in its state of motion. This property is called inertia.

(a) Moment of force can be reduced by reducing the distance between force and the turning point.

(b) Moment of force can be increased by increasing the distance between force and the turning point. 

Law of moments : In equilibrium sum of anticlockwise moments is equal to sum of clock-wise moments. Sum of anticlock wise moments = sum of clockwise moments.

The product of mass and velocity of the body is called linear momentum. S.I. unit of linear momentum is kg m s^-1.

When a number of forces acting on a body produce no change in its state of rest or of motion, the body is said to be in equilibrium.

When number of forces acting on a body, keep it in equilibrium, then the sum total of clockwise moments about any turning point is equal to sum total of anticlockwise moments about the point. 

(i) When a body remains in the state of rest under the influence of the applied forces, the body is in static equilibrium. For example a book lying on a table is in static equilibrium.

(ii) When a body remains in the same state of motion (translational or rotational), under the influence of the applied forces, the body is said to be in dynamic equilibrium. For example, a rain drop reaches the earth with a constant velocity is in dynamic equilibrium.

For a body to be in equilibrium:

(i) The resultant of all the forces acting on the body should be equal to zero.

(ii) The resultant moment of all the forces acting on the body about the point of rotation should be zero.

(a) 1kg × 9.8ms^-2 

The rate of change of momentum of a body is directly proportional to the force applied on it and this change in momentum takes place in the direction of the applied force, i.e.,

F ∝ Δp/Δt, ΔP/Δt

Where p denotes momentum and Δp is the change in momentum in time Δt.

(a) Mass X change in velocity = Force x time interval.

(b) The mass of a body remains constant till the velocity of body is Much less than the velocity of light.

Newton's second law of motion - The rate of change of momentum of a body is directly proportional to the force applied on it and this change in momentum takes place in the direction of the applied force, i.e.,

F ∝ ΔP/Δt

where p denotes momentum and Δp is the change in momentum in time Δt.

When mass m of the body is constant at velocity v (which is much smaller than the velocity of light c) then rate of change of momentum is:

F = Δ/Δ = m (Δ/Δ) = ma

F = ma

Force = 64kgf = 64 x 10N

acc. a = 2ms^-2

∴ mass = f/a = (64 x 10)/2 = 320kg

 (i) The wastage of energy should be avoided. 

(ii) The excessive use of non-renewable resources such as coal, petroleum and natural gas should be reduced. 

(b) decreases

Advantages: 

(i) A very small amount of nuclear fuel produces huge amount of energy. 

(ii) Nuclear fuel does not contribute harmful greenhouse gases to the atmosphere on burning. 

Disadvantages: 

(i) The waste that is produced when using nuclear fuel is radioactive and very harmful. It needs to be disposed of carefully. 

(ii) World uranium supplies may run out in about 50 year. 

Initial potential energy = mgh 

Final potential energy = mg × 2h = 2mgh 

Increase in potential energy = Final potential energy – Initial potential energy 

= 2mgh – mgh = mgh.