Concept of Net Force

# Our Objective

To understand the concept of net force.

# The Theory

### What is force?

A force is a push or pull on an object. It is a consequence of interaction between two objects and usually results in some change in the state of motion of an object. Actions like picking, opening, shutting, kicking, hitting, lifting, flicking, etc., are the different ways in which you can apply strength or energy to the object. Each of these actions can be grouped as a pull or a push or both.

When something is pushed, it moves in the direction of the push. The harder you push, the further the item moves away from you. Pulling is a similar action where you hold and move someone or something in a particular direction and especially toward yourself. A force can range from being extremely weak to being extremely strong. You only need to apply small muscular force in lifting your pen from the table. Meanwhile, you must exert a lot of energy and strength or apply a large force in order to move a heavy box.

The effect of forces on an object:

• Force can make things move.
• It can change their speed.
• Change their shape.
• Change the direction of motion.

### Types of forces:

There are two types of forces – Contact forces and Non-contact forces.

### Contact Forces

Contact forces happen when objects touch each other. Some examples of contact forces are:

• Applied Force: A force with which an object is pushed or pulled. Here a force is applied to an object either by a person or by any other object. Example: A person pushing a chair to the other side of the room, person kicking a ball.
• Frictional Force: Friction is a force caused when one object rubs against another or when an object moves across a surface. The force of friction always acts on all the moving objects and its direction is always opposite to the direction of motion. Example: A book sliding on the table, a ball rolling on the floor, when you push your bed forward, when you pull the suitcase of clothes, you need it from under the bed.
• Air Resistance Force: It is a type of frictional force acting on objects moving through the air. The air resistance opposes the movement of the object, slowing it down. As the speed of object increases, the air resistance also increases. Example: An airplane or a parachute moving up in the sky, while riding a bicycle, the rider can feel a force of friction exerted by the air.
• Tension Force: Tension is the force exerted by a string, rope, or chain when it is pulled tightly by another object on the opposite end. This force acts along the length of the wire or rope. Only one of these two objects is flexible, while the other is rigid. Example: Climbing a mountain using a rope, the chandelier or wind chimes hanging from the ceiling.
• Spring Force: It is the force a spring uses to return to its original length after being compressed or stretched. Example: While jumping on a trampoline, the set of springs attached to the fabric are extended due to your body weight. The force exerted as the spring tries to regain its original position launches you into the air.

### Non-contact Forces

The forces that act between two objects at a distance are non-contact forces. Such forces occur when an object is able to push or pull another object even when they are not in contact with each other. Some examples of non-contact forces are:

• Gravitational Force: The force by which the earth attracts objects towards it is known as gravitational force. All objects on the Earth experience gravitational force and fall towards the earth. Example: Leaves and fruits fall from a tree downwards towards the ground, a ball thrown up in the air comes back down.
• Magnetic Force: The push or pull exerted by a magnet is called magnetic force. Example: Iron nails placed near a magnet are attracted by it, like poles (South-South or North-North) of two magnets repel each other.
• Electrostatic Force: The force exerted by a charged body on another charged or uncharged body is known as electrostatic force. It is one of the fundamental forces of the Universe. Example: The crackling sound produced while taking off woollen clothes is due to the electrostatic force developed between the fabric layer and the skin. After combing your hair, the comb picks up small pieces of paper placed near it.

### Net Force

There may be several forces acting on an object. The combined effect of all these forces acting on an object is known as the net force. If these forces are applied on an object in the same direction, the forces add to one another resulting in a larger force. If the two forces act in the opposite directions on an object, they cancel each other and the net force acting on it is the difference between the two forces.

A force could be larger, smaller than the other or equal to each other. In case the forces acting on the opposite directions are equal, then the net force on an object is zero. This is known as a balanced force. Such an object remains at rest or continues to move with a constant speed. It is the unbalanced force that makes an object move or increase its speed.

The strength of a force is usually expressed by its magnitude. We have also to specify the direction in which a force acts. If the direction or the magnitude of the applied force changes, its effect also changes. The force is measured in a unit called the newton, which is abbreviated as "N". In science, forces are usually represented by arrows. The direction of the force will be shown by an arrow in that same direction.

# Learning Outcomes

• Students learn about forces and its types.
• Students understand the concept of net force.
• Students learn to distinguish contact and non-contact forces.