# Chapter 14 : Force and Motion

### Topics covered in this snack-sized chapter:

#### Force arrow_upward

• Force is the process that cause any object to undergo some sort of changes.
• Force is the push or pull you apply to make things move.
• • A force can:
• Make an object move.
• Change the direction of a moving object.
• Stop a moving object.
• Force can also change the shape of an object.
• Force is also defined as Mass and acceleration vector product.
• The ratio of speed over time gives Acceleration of the motion.

• #### Types of force arrow_upward

###### Applied Force

• An applied force is a force that is applied to an object by a person or another object.
• If a person is pushing a desk across the room, then there is applied force acting upon the object.

• ###### Gravitational Force

• The force of gravity is the force with which the earth, moon, or other massively large object attracts another object towards itself.
• This is the weight of the object.
• All objects upon earth experience a force of gravity.
• It is directed "downward" towards the center of the earth.

• ###### Normal Force

• The normal force is the support force exerted upon an object that is in contact with another stable object.
• On occasions, a normal force is exerted horizontally between two objects that are in contact with each other.
• For instance, if a person leans against a wall, the wall pushes horizontally on the person.
• ###### Friction Force

• The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it.
• The friction force often opposes the motion of an object.

• ###### Tension Force

• The tension force is the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.
• The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.
• #### Balanced Forces arrow_upward

• Two equal and opposite forces applied on an object are called balanced forces.
• For example pushing and pulling the object with same force on both sides as shown in the figure.
• • Forces are shown by arrows in diagram. The direction of the arrow shows the direction in which the force is acting.
• If two forces are balanced, it means that both the forces are equally applied but are acting in opposite directions.
• Balanced forces do not change motion
• If two balanced forces are acting on an object, that object will not change its motion. If it is still, it will stay still.
• If it is moving, it will continue moving, in the same direction and at the same speed.

• #### Unbalanced forces arrow_upward

• Unbalanced forces do change the way something is moving.
• Unbalanced forces can make objects start to move, speed up, slow down, or change direction.
• #### Friction arrow_upward

• The friction force acts in a direction parallel to the area of contact, and opposes the motion or the tendency to move.
• There are two types of friction force:
• Sliding friction
• Static friction
• Friction results when the two surfaces are being pressed together closely.
• It is because of intermolecular attractive forces between molecules of different surfaces.
• • As such, friction depends upon the nature of the two surfaces and upon the degree to which they are pressed together.

• ###### Sliding Friction

• Sliding friction results when an object slides across a surface.
• Sliding friction results when object is in motion so it is also known as Kinetic Friction.

• ###### Static Friction

• Friction forces can also exist when the two surfaces are not sliding across each other. Such friction forces are referred to as static friction.
• Static friction results when the surfaces of two objects are at rest relative to one another and a force exists on one of the objects to set it into motion relative to the other object.

• #### Motion arrow_upward

• Motion is a change in position of an object with respect to time.

• ###### Kinds of Motion

• We can classify the motion of bodies as:
• Translatory (linear)
• Rotatory
• Vibratory or Oscillatory
• Circular
• Periodic
• Random

###### Translatory Motion

• The motion of an object is said to be translatory if the position of the object is changing with respect to a fixed point or object.
• Example:
• A boy running
• A car moving

###### Rotatory Motion

• Motion is said to be rotatory when the object rotates on its own axis
• Example:
• Spin Top
• CD or DVD playing

###### Oscillatory Motion

• Oscillatory Motion is repetitive and fluctuates between two locations.
• The to and fro motion of an object about a fixed point is called oscillatory motion or vibratory motion.
• Example:
• Seesaws
• Clock pendulum

###### Circular Motion

• A motion in which the body traverses a circular path is called Circular Motion.
• This is a kind of translatory motion where the body reaches the initial position each time it completes traversing the circle.
• Example:
• Hands of a clock

###### Periodic Motion

• Any motion that repeats itself at regular intervals of time is called Periodic Motion.
• Example:
• Heart beat
• A water wave

###### Random Motion

• Irregular Motion of bodies changing the nature of motion frequently is called Random Motion.
• Example:
• Motion of football player on the ground
• A flying butterfly

#### Newton's Laws of Motion arrow_upward

###### Newton's First Law of Motion

• An object at rest will remain at rest unless acted on by an unbalanced force.
• An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
• This law is often called "the law of inertia".
• ###### Newton's Second Law of Motion

• Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
• It can be expressed as a mathematical equation:
• Force=Mass × Acceleration ###### Newton's Third Law of Motion

• For every action there is an equal and opposite re-action.
• #### Thank You from Kimavi arrow_upward

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