Toer conservation of energy

Notes for teachers (optional)

Energy is the basis of human life. Every single aspect of human experience whether it be in the external world or what we do or what is done to us can be adequately described either as a transfer of energy in one form from one place to another or the transformation of energy from one form to another.

What is the meaning of energy? How does one measure it? What are the various forms in which energy manifests itself? How is energy obtained and transformed from one form to the other? How can energy be conserved? How do the production and utilization of energy in its various forms affect our environment? What is the source of all energy? What kind of energy flows and conversions take place in the environment?

Energy, types of energy-Kinetic and potential

When an object is moved against a force, work is done and energy is spent in the process. Thus we say “A person must have a lot of energy to do a hard day’s work”. In fact one way to define energy is: Energy is the capacity to do work.

The word ‘energy’ is derived from the Greek energia'''-en means '''‘in’''' and ergon''', means '''work.

Energy is defined for an object in a particular state. When work has been done on an object, its energy changes. At a very basic level, there are two forms of energy – kinetic energy and potential energy.

For example, a block is lying at rest on a table. It is pushed and it acquires a uniform velocity. Now the block has acquired some energy (kinetic energy, as we will define shortly). While the cause of the change in the state was a force (the push), it has resulted in the body acquiring a change in energy.

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We can see that there are two ways of describing this (and for that matter, any) process. One is to study the cause (the force) and the other is to examine the change in energy.

Biological energy flow

We saw earlier that energy flows constantly through the Earth and its environment. Plants fix the solar radiation into carbohydrates and form the basis of much of the energy flow in the world. Either through the food chain or through the accumulation as fossil fuels, this accounts for the bulk of the energy in the world. We cannot discuss energy without discussing the connection with food and how energy flows through living organisms through food. This flow of energy through living organisms is called a food chain.

Energy flow in an ecosystem

An ecosystem is a community where living and non-living things interact. There are two main processes in an ecosystem – energy flow and nutrient flow. The energy flow in an ecosystem happens through the food chain.

Teaching Outlines

Concept 1 : Energy is ability to do work

Activity 1 – Energy is ability to do work

/home/ranjani/Desktop/Conservation of energy/energy.ogv

Concept 2 : Conservation of energy

Activity 1 - Conservation of mechanical energy in a pendulum

Pre-requisites

Availability of computer, projector, simulation

Prior discussion on forms of energy

Method:

Use the PhET simulation Pendulum Lab.

For this we will need to open an application called PhET on the computer. You can find PhET under Applications> Education> Science. PhET is an educational resource that contains computer demonstrations of experiments and activities. When we click on Play with sims – it will open simulations in various subjects. We will click on Physics and scroll down to the simulation on Pendulum Lab.

When we want to open a simulation, we click on the green rectangle which says “Run Now”.

After running the simulation show the following video /home/ranjani/Desktop/Conservation of energy/Conservation of Energy in simple pendulum.VOB

Discussion question for activity

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Notes (optional)

The motion of a pendulum is a classic example of mechanical energy conservation. A pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion. Neglecting air resistance (which would indeed be small for an aerodynamically shaped bob), there are only two forces acting upon the pendulum bob. One force is gravity. The force of gravity acts in a downward direction and does work upon the pendulum bob. However, gravity is an internal force (or conservative force) and thus does not serve to change the total amount of mechanical energy of the bob. The other force acting upon the bob is the force of tension. Tension is an external force and if it did do work upon the pendulum bob it would indeed serve to change the total mechanical energy of the bob. However, the force of tension does not do work since it always acts in a direction perpendicular to the motion of the bob. At all points in the trajectory of the pendulum bob, the angle between the force of tension and its direction of motion is 90 degrees. Thus, the force of tension does not do work upon the bob.

Since there are no external forces doing work, the total mechanical energy of the pendulum bob is conserved.

Concept 5 : Energy flow in an ecosystem

Activity 1: Energy flow through a food chain

Method

Watch the following videos on food chain

Notes (optional)

The laws of thermodynamics we saw earlier govern the processes in a food chain also. For example, the first law tells us that an organism can only use the energy it receieves whereas the second law tells us that not all of the energy received by an organism can be used – some of it will be lost as heat. At each level of the food chain, the amount of energy that gets transferred to the next trophic level is only a portion of the energy present in the lower level. This fraction varies widely across ecosystems. When finally organisms die and decay they pass the materials of life in simple forms to other organisms (nutrient flow). This energy flow is not cyclic – continuously less and less energy is available. So then, how do ecosystems continue? They depend on an external source of energy called the Sun. If the Sun's energy is not available in usable form, life on Earth may not be possible any longer.