Types of Forces - Class 4 Notes & Olympiad Questions

Force

a) Force is a push or a pull that one object applies to another object when they interact.
b) When you push something, you make it move away from you. When you pull something, you bring it closer to you.
c) We use force in many activities we do, like walking, lifting objects, throwing things, and moving objects from one place to another.
d) Force can make objects start moving, stop moving, or change their direction or speed.
e) There are two types of forces: contact forces and non-contact forces.
f) Contact forces occur when two objects physically touch each other, like when a person kicks a ball.
g) Non-contact forces happen between objects that are not physically touching each other, such as gravitational force (which keeps us on the ground) or magnetic force (which makes magnets stick together).

Effects of Force

1. Move a stationary object: If a force is applied to an object at rest, it can make the object start moving. For example, pushing a stationary car can make it move.

2. Stop a moving object: A force can also be used to stop a moving object. For instance, applying brakes to a bicycle or a car can slow it down and eventually bring it to a stop.

3. Change the speed of a moving object: When a force is applied to a moving object, it can either speed it up or slow it down. For example, pushing a swing can make it go faster while applying a braking force to a bicycle can make it slow down.

4. Change the direction of a moving object: By applying a force at an angle to the direction of motion of an object, you can change its path or direction. For instance, kicking a soccer ball in a different direction can change its course.

5. Change the shape and size of an object: Forces can cause objects to deform or change their shape and size. For example, squeezing a soft ball can change its shape temporarily.

Friction

a) Friction is the resistance that occurs when two objects rub against each other.
b) Whenever two objects come in contact and move against each other, they create friction.
c) Friction acts in the opposite direction to the motion of the objects, trying to slow them down or prevent their motion.
d) The amount of friction depends on the surfaces of the objects involved. Smoother surfaces usually have less friction, while rough surfaces generate more friction.
e) Friction can also vary depending on the type of motion. Rolling objects experience less friction compared to sliding objects.
f) Friction is present in many everyday activities, such as walking on the ground, riding a bike, or sliding down a slide. It helps us maintain control and prevents us from slipping.

Types of Forces

1. Gravitational Force

a) The force that pulls every object towards the Earth is called the force of gravity or gravitational force.
b) Gravity is the reason why objects are pulled downwards towards the Earth's surface.
c) Gravity acts on all objects, whether they are in motion or at rest.
d) When we throw a ball upwards, it eventually comes back down to the ground. This is because the Earth's gravity is pulling the ball back towards it.

2. Frictional Force

a) Frictional force is the force that acts between two surfaces in contact and opposes the relative motion or tendency of motion between them.
b) When two objects are in contact and one tries to move or slide over the other, the frictional force comes into play, resisting the motion.
c) For example, when you stop pedalling a bicycle, it gradually slows down and eventually comes to a stop. This happens because there is a force of friction acting between the tires of the bicycle and the road, which slows down the bicycle's motion.
d) The presence of substances like oil or grease can reduce the frictional force between surfaces, making them slide more easily.
e) Frictional force is also present when you write with a pen or pencil on paper. The friction between the tip of the pen/pencil and the paper allows you to create marks.
f) Frictional force helps us to walk without slipping and enables us to grip objects.

3. Muscular Force

a) Muscular force refers to the force generated by our muscles when they contract and exert a push or pull on an object.
b) We use muscular force to perform various physical activities such as walking, running, pushing, throwing, pulling, and lifting objects.
c) For example, when you kick a ball, the force exerted by your leg muscles provides the necessary push to set the ball in motion.

4. Magnetic Force

a) Magnetic force is the force of attraction or repulsion exerted by a magnet on other magnetic or magnetisable objects.
b) When a magnet is brought near small iron clips or other magnetic materials, the magnetic force causes them to be attracted to or repelled from the magnet.
c) For instance, when you bring a magnet close to a pile of iron clips, the clips get attracted to the magnet and stick to it due to the force of magnetism.
d) Magnetic force plays a vital role in various applications, including the functioning of compasses, electric motors, and magnetic storage devices like hard drives.