Forces

Forces

By Restie Carullo

​Most of the motions we come across in our daily life are non-uniform and the primary cause of changes in motion is FORCE. Force is simply defined as a push or a pull in an object. It can move, slow down, speed up, or stop the motion of an object.

Multiple Choice

Whenever there is an interaction between two objects, there is a force upon each of the objects.

• True

• False

​Classification of Force

Classification of Force

​1. Contact Force

​Contact Force is a force that is applied by objects in contact with each other. Contact force acts on a point of direct contact between the two objects. Contact force is responsible for most of the interactions we experience in our daily lives.

Contact Force

​Types of Contact

Force:

a. applied

b. friction

c. normal​

Contact Force

​Applied Force: Force which is applied to an object by another object. A person pushing a barrel is an example of applied force. When the person pushes the barrel then there is an applied force acting upon the barrel. The applied force is the force exerted on the barrel by the person and it is responsible for the motion of the barrel. Applied force may be contact force as well as non – contact force

Contact Force

​Frictional Force: Friction is a force exerted by a surface against the motion of a body across its surface. If a book slides across the surface of a desk, then the desk exerts a friction force in the opposite direction of its motion causing it to stop sliding after a finite distance. Friction is a type of contact force only.

Contact Force

​The normal force is also called Support force. The normal force is the support force exerted upon an object that is in contact with another fixed or stable object. For example, if a book is resting upon a surface, then the surface is exerting an upward force upon the book in order to support the weight of the book. The solid ground provides the normal force for all of us live. The normal force is proportional to the weight of the body. Larger the body larger the normal force. If a very high weight is kept on a table and it cannot provide a normal force that large, then it breaks.

Classification of Force

​2. Non-Contact Force

​Non-contact forces are forces that act between two objects that are not physically touching each other.

​A gravitational force is experienced by any mass in a gravitational field. Masses are attracted towards each other by gravity.

​Electrostatic force: An electrostatic force is experienced by any charged particle in an electric field.

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Non-Contact Force

​Electrostatic Force

Non-Contact Force

Gravitational Force

Force Exercises

Multiple Choice

A car braking is an exmaple of what type of force?

• Gravity

• Air Resistance

• Friction

Multiple Choice

What is the name of the force that pulls you to the earth?

• Gravity

• Air Resistance

• Friction

Multiple Choice

Rubbing a balloon on your head causes charge to build up on the balloon The balloon can then "stick" to the wall - what force is acting here?

• Gravity

• Electrostatic

• Friction

• Applied

Multiple Choice

What is the name of the force responsible for keeping a book on the desk?

• Gravity

• Air Resistance

• Normal Force

• Friction