Chapter 14 : Force and Motion
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.
Topics covered in this snack-sized chapter:
A force can:
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.
- Change the direction of a moving object.
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.
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.
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.
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.
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.
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 do change the way something is moving.
Unbalanced forces can make objects start to move, speed up, slow down, or change direction.
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:
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 results when an object slides across a surface.
Sliding friction results when object is in motion so it is also known as Kinetic 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.
is a change in position of an object with respect to time.
We can classify the motion of bodies as:
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.
Motion is said to be rotatory when the object rotates on its own axis
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.
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.
Any motion that repeats itself at regular intervals of time is called Periodic Motion.
Irregular Motion of bodies changing the nature of motion frequently is called Random Motion.
- Motion of football player on the ground
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 First 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:
Newton's Second Law of Motion
Force=Mass × Acceleration
For every action there is an equal and opposite re-action.
Newton's Third Law of Motion