What is Energy?
taught by By Anja Drazenovic,
Matea Mirkovic,
Danijela Cavcic,
Mirjana Cetinski(Croatia)
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Everything that happens around us is caused by a kind of energy. Let's look out the window! The sun is shining and giving us light and heat energy.
When the wind blows, its energy moves the clouds, branches and the waves on the sea. Electrical energy lights our streets and homes at night and make many devices to work.
When my father drives a car, he can do it by petrol which is a stored energy.
The food we all eat contains energy. That energy helps us to live, learn and play.
So, the energy is the ability to do some work.
There are different forms of energy:
- Electical energy
- Heat or Thermal energy
- Chemical energy
- Mechanical energy
- Light or Radiant energy
- Nuclear energy
There are 2 types of energy:
- Potential energy (stored energy)
- Kinetic energy (moving energy)
Let's try this simple example to learn about the two types of energy.
1. Put your Physics book at the edge of the desk and push it off to the floor. The moving book uses kinetic energy .
2. Now, pick up the book and put it back on the desk. You used your own energy to lift and move the book. Moving it higher than the floor adds energy to book. As it stays on the desk, the book has potential energy . If the book is on a higher position, it will fall further. That means the book has more potential energy.
What is Kinetic Energy ?
All objects that are moving possess energy which depends on their mass and their speed. This enery is called kinetic energy .
Let's calculate the kinetic energy E k of an object using this relation
Ek = 1/2mv 2
m stands for its mass
v stands for its speed
When the mass is in kilograms (kg), and the speed is in metres per second (m/s), the energy is in joules (J).
ACTIVITY
Create the graph that shows the amount of kinetic energy (in joules) that a 40kg girl would have if she moves at speeds up to 5m/s.
- How much kinetic energy will a 40kg girl have when running at 6m/s?
- How much kinetic energy will a 40kg girl have when jogging at 2m/s?
- How fast would a 40kg girl need to run to have 500J of kinetic energy?
- How fast would a 40kg person need to run to have twice the kinetic energy as the girl in the question 3?