Forms of Energy (Chapter 5 Lesson 1)

Learning Targets:
What is energy?
What are potential and kinetic energy?
How is energy related to work?
What are different forms of energy?

When you hear the word, "Work," what is the first thing you think of? Maybe sitting at a desk? Maybe plowing a field? Maybe working out? Work is a word that has a little bit of a different meaning in Physics and today, Shini is going to walk us through it. Also, Energy and Power

You will learn about "Force, Work and Energy" in this video.

Force is the push or pull applied on an object. It can move a stationary object or stop a moving object. Force can also change the speed and direction of a moving object. If enough force is applied, it can also change the shape or size of an object.

When force is applied on an object, resulting in the movement of that object, work is said to be done. Work can be calculated using the formula, Work done = Force x Distance.

The ability or the capacity to do work is called energy. The food that we eat gives us energy to do various activities.

You will learn about "Potential and Kinetic Energy" in this video. The law of conservation of energy states that energy cannot be created or destroyed, it can only be converted from one form to another.

Potential energy is energy due to position while kinetic energy is energy due to motion. The unit of energy is joules.

To understand this better, let us take an example. Look at this pendulum. When we hold it on one side, at that time, it has a certain amount of potential energy. When the pendulum is released, this potential energy starts getting converted to kinetic energy. As the pendulum moves back and forth, the kinetic energy is converted to potential energy and vice versa until the pendulum stops.

The formula for potential energy is mgh, where m = mass, g = acceleration due to gravity and h = height. If we climb on top of a tree, the potential energy possessed by us will be mgh. Here, if we assume mass = 30 kg, acceleration due to gravity = 9.8 m/s^2 and height of the tree as 20 metres, then the potential energy would be 30 * 9.8 * 20 = 5880 joules.

At the top, the K.E. is zero. If we jump, then the stored potential energy starts getting converted to kinetic energy. Just before we land, all of the potential energy gets converted to kinetic energy. Now, the potential energy = 0. The kinetic energy can be calculated using the formula, 1/2mv^2 where m = mass and v = velocity.

You will learn about "Introduction to Light" in this video. Light is a form of energy that enables us to see all the things around us.

The main source of light on the earth is the sun. Plants are able to prepare their own food using sunlight.

Some other objects also give out light. They are known as luminous objects. For example, bulbs, lamps, candles etc are luminous objects.

While there are some objects that do not give out light. They are known as non-luminous objects. For example table, cloth, bag, utensils etc. are non-luminous objects.

Non-luminous objects are generally of two types, transparent objects and opaque objects.

Transparent objects are those that allow light to pass through them, like glass, water etc.

While, Opaque objects are those that do not allow light to pass through them, like wood, stone etc.

You will learn about "Electromagnetic Induction" in this video. Michael Faraday was a scientist who was curious to know whether a magnetic field could produce a current. He set up an experiment in which he took a coil having many turns and connected it to a galvanometer. He then took a magnet and held it next to the coil. The needle of the galvanometer showed no deflection. Now he started moving the magnet close to of the coil. The needle of the galvanometer started deflecting, indicating that current was being induced in the coil. However, when he stopped moving the magnet, the needle also stopped deflecting.

Then, he kept the magnet fixed and moved the coil. He again saw deflection. This made him realize that current was induced in the coil due to relative motion between the magnet and coil. Now, he moved the magnet away from the coil. As a result, the needle of the galvanometer deflected in the opposite direction. This meant the current was now being induced in the opposite direction.

Michael Farday then wanted to see whether speed played a role as well or not. He started moving the magnet faster towards the coil. He saw that faster motion of the magnet led to faster needle deflection. That meant rate at which current was induced was more. He then decided to reverse the poles of the magnet. He noticed that deflection reversed when the poles reversed.

After doing all these experiments, Michael Faraday gave to the world, Faraday's law of electromagnetic induction. This production of electric current across a conductor when exposed to a changing magnetic field is known as electromagnetic induction.