Newton's laws of motion
Newton’s laws of motion first stated by English physicist and mathematician Sir Isaac Newton. Laws are about relations between the forces acting on a body and the motion of the body.
Newton’s first law states that, if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force.
Newton’s second law is a quantitative description of the changes that a force can produce on the motion of a body. It states that the time rate of change of the momentum of a body is equal in both magnitude and direction to the force imposed on it. The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction. A force applied to a body can change the magnitude of the momentum, or its direction, or both. Newton’s second law is one of the most important in all of physics.
For a body whose mass m is constant, it can be written in the form F = ma, where F (force) and a (acceleration) are both vector quantities. If a body has a net force acting on it, it is accelerated in accordance with the equation. Conversely, if a body is not accelerated, there is no net force acting on it.
Newton’s third law,
This law states that to every action there is always an equal and opposite reaction.
UCM(Uniform circular motion)
A body moving in a circle of constant radius with a constant speed has a non-zero force acting on it. This force is known as Centripetal force. It is directed towards the center of the circle. Its value is given by the formula: F=mv2/R.
1. When an object tied at the end of a string is whirled in a horizontal circle, the necessary centripetal force for maintaining circular motion is provided by tension in the string.
2. If a car is traveling round a circular horizontal road with uniform speed, the necessary centripetal force for negotiating the curve is provided by force of friction between tyres of vehicle and road surface.
3. The necessary centripetal force is provided by push due to rails on the wheels of train during taking turn.
4. Moon revolves around the earth in circular orbit. Here the necessary centripetal force is provided by gravitational force of attraction between moon and earth.
Friction is defined as the force that opposes the motion of a solid object over another. There are mainly four types of friction: static friction, sliding friction, rolling friction, and fluid friction. ... Similarly, if VR < VL then the point B tends to move forward and hence the friction acts in the backward direction.
Types Of Friction
Following are the friction types which depend on the types of motion:
- Static Friction
- Sliding Friction
- Rolling Friction
- Fluid Friction
Static Friction
Static friction is defined as the frictional force that acts between the surfaces when they are at rest with respect to each other.
The magnitude of the static force is equal in the opposite direction when a small amount of force is applied. When the force increases, at some point maximum static friction is reached.
Static Friction Examples
Following are the examples of static friction:
- Skilling against the snow
- Creating heat by rubbing both the hands together
- Table lamp resting on the table
Coefficient Of Static Friction
The coefficient of static friction is denoted as µs. The maximum force of static friction is given as the product of the coefficient of static friction and normal force and force of static friction is less than or equal to the product of the coefficient of static friction and normal force. It is given as:
| Fs max = µs η and Fs ≤ µs η |
Where,
- Fs is the force of static friction
- µs is the coefficient of static friction
- η is the normal force
- Fs max is the maximum force of static friction
Sliding Friction
What Is Sliding Friction?
Sliding friction is defined as the resistance that is created between any two objects when they are sliding against each other.
Examples Of Sliding Friction
Following are the examples of sliding friction:
- Sliding of the block across the floor
- Two cards sliding against each other in a deck
Coefficient Of Sliding Friction
The coefficient of sliding friction is denoted as µs. The force of sliding friction is defined as the product of the coefficient of sliding friction and the normal force. It is given as:
| Fs = µs. Fn |
Rolling Friction
What Is Rolling Friction?
Rolling friction is defined as the force which resists the humanmotion of a ball or wheel and is the weakest types of friction.
Examples Of Rolling Friction
Following are the examples of rolling friction:
- Rolling of the log on the ground
- Wheels of the moving vehicles
Coefficient Of Rolling Friction
The coefficient of rolling friction is denoted as µr. The force of rolling friction is defined as the product of the coefficient of rolling friction and the normal force. It is given as:
| Fs = µr. Fn |
Fluid Friction
What Is Fluid Friction?
Fluid friction is defined as the friction that exists between the layers of the fluid when they are moving relative to each other.
Examples Of Fluid Friction
Following are the examples of fluid friction:
- The flow of ink in pen
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