Video Lesson

Lesson objective

Dear learners,

At the end of the lesson you will be able to

• Discuss what the concept of force means in physics, and why forces are vectors.
• Define force and discuss its effects on a body.
• Distinguish between contact forces and field forces.
• Discuss the four fundamental forces in nature and their real life application.

Brainstorming Question

1. How do you define the term force in your own words? Mention some of the natural phenomena that show the action of a force on or between objects in your surroundings.
2. How does force affect every moment in your life?

Key Terms and Concepts

The concept of force

• Dynamics is the study of motion and its causes,
• Force is the push or pull on an object with mass that causes it to change its velocity
• Push and pull are caused by objects interacting with one another.
• Push is described as an action of force that causes an object to move from its initial position.
• Pushing the table, Pushing thumb pins, Walking, etc. are examples of Push.
• The pull is described as an act that makes anything move by tugging or dragging.
• Plucking the string of a guitar, Opening the drawer, Pulling ropes while playing tug of war, etc. are examples of Pull.
• Force is a vector quantity.
• The SI unit of force is Newton (N).
• The dimensional formula of force is [M L T^-2].
  • 1 Newton is equivalent to 1 kg m/s²
  • 1 Newton is defined as the force required to accelerate a body of mass 1 kg with acceleration 1 m/s².

Effects of Force

The following are the effects of force

• Force can change the state of the rest of a body.
• It can change the state of motion of the body.
• It can change the direction of the body.
• It can change the shape and size of the body.

Types of Force

The following are the different types of force

Contact Force

Contact forces:- are forces that result from physical contact between two bodies. 

The following are some examples of contact forces:

• Muscle Power
• Mechanical Force
• Force of Friction
• Tension Force
• Viscous Drag
• A girl stretching a spring,
• a man pulling a box on the floor, and
• a girl kicking a ball

Non-Contact Force

Non-contact forces or field force :-are those that work across spaces without making direct touch with the body. 

The following are some examples of non-contact forces:

• Gravitation Force
• Electrostatic Force
• Magnetic Force

Fundamental forces in nature

The known fundamental forces in nature are all field forces. These are, in order of decreasing strength:

1. The strong nuclear force between subatomic particles;
2. The electromagnetic forces between electric charges;
3. The weak nuclear force, which arises in certain radioactive decay processes; and
4. The gravitational force between objects.

• The strong force keeps the nucleus of an atom from flying apart due to the repulsive electric force of the protons.
• The weak force is involved in most radioactive processes and plays an important role in the nuclear reactions that generate the Sun’s energy output.
• The strong and weak forces operate only on the nuclear scale, with a very short range on the order of 10-15 m.

Balanced and Unbalanced Forces

When balanced forces are applied to a body, there is no net effective force acting upon it. Balanced forces do not cause any changes in motion.

Unbalanced forces exerted on a body change its velocity and/or direction of motion. It moves in the direction of the force with the highest magnitude.

Net Force

When many different forces act on a body, they can be resolved into a single component called the net force acting on the body. The net force determines the direction of motion.

Weight

Weight is the gravitational force with which the earth pulls an object. It is given by

Weight (W) = mg

Where

• m is the mass of the body
• g is the acceleration due to gravity

Normal Reaction

Normal reaction is a force between the surfaces in contact.

• This force is normal to the surfaces in contact.
• The normal reaction occurs to stop two bodies in contact to merge into each other.