# Work

 Page 1 / 3

## Introduction

Imagine a vendor carrying a basket of vegetables on her head. Is she doing any work? One would definitely say yes! However, in Physics she is not doing any work! Again, imagine a boy pushing against a wall? Is he doing any work? We can see that his muscles are contracting and expanding. He may even be sweating. But in Physics, he is not doing any work!

If the vendor is carrying a very heavy load for a long distance, we would say she has lot of energy. By this, we mean that she has a lot of stamina. If a car can travel very fast, we describe the car as powerful. So, there is a link between power and speed. However, power means something different in Physics. This chapter describes the links between work, energy and power and what these mean in Physics.

You will learn that work and energy are closely related. You shall see that the energy of an object is its capacity to do work and doing work is the process of transferring energy from one object or form to another. In other words,

• an object with lots of energy can do lots of work.
• when work is done, energy is lost by the object doing work and gained by the object on which the work is done.

Lifting objects or throwing them requires that you do work on them. Even making electricity flow requires that something do work. Something must have energy and transfer it through doing work to make things happen.

## Work

Work

When a force exerted on an object causes it to move, work is done on the object (except if the force and displacement are at right angles to each other).

This means that in order for work to be done, an object must be moved a distance $d$ by a force $F$ , such that there is some non-zero component of the force in the direction of the displacement. Work is calculated as:

$W=F·\Delta xcos\theta .$

where $F$ is the applied force, $\Delta x$ is the displacement of the object and $\theta$ is the angle between the applied force and the direction of motion.

It is very important to note that for work to be done there must be a component of the applied force in the direction of motion. Forces perpendicular to the direction of motion do no work.

For example work is done on the object in [link] ,

## Investigation : is work done?

Decide whether on not work is done in the following situations. Remember that for work to be done a force must be applied in the direction of motion and there must be a displacement. Give reasons for your answer.

1. Max pushes against a wall and becomes tired.
2. A book falls off a table and free falls to the ground.
3. A rocket accelerates through space.
4. A waiter holds a tray full of meals above his head with one arm and carries it straight across the room at constant speed. (Careful! This is a tricky question.)

formula of heat reaction
final energy-initial energy of substances
Chantel
what is the difference between ethene and ethane
Ethane is a saturated organic molecule while ethene is unsaturated Ethane has 2 carbon atoms and 6 hydrogen atoms, while ethene has 2 Carbons and 4 hydrogens Ethane has single bond between the 2 Carbon atoms while ethene has double bond
Rito
How do you know that the reaction is in acid medium or basic medium
What formular is used when source and Observer are moving towards to each other
put a + on top n - on the bottom
Sanele
what is doppler effect?
doppler effect is the perceived change in frequency of a sound caused by either the source or the listener
Qaqamba
moving relative to each other
Qaqamba
A Catalyst is a chemical substance that speeds up a chemical reaction.
It does this by lowering the activation energy.
Sheron
what is exothermic
reaction that releases energy
Beauty
what is a catalyst
Joseph
Catalyst is to speed up the reaction
CELO
catalyst is a substance added into a solution to speed up the process
Joseph
As it speeds up the reaction by lowering the activation energy, it does not take part in the reactants or products formed
Rito
reaction that release energy
Qaqamba
what is exothermic
reaction that gives off heat to the surroundings
Thabile
formula for calculating the heat of reaction
Anelisiwe
I need help in electrostatic
in exactly in electrostatic
Beauty
send the question on electrostatic maybe I can help
Beauty
factors affecting the rate of reaction
hi
Xiluva
hi
Mashweme
hey
Musa
I'm xiluva ...do we help those who are having challenges on their studies?
Xiluva
I mean on physical science
Xiluva
I believe it's supposed to be like that. Helping those who are having educational challenges
Rito
Yep physical sciences more specifically
Rito
ok ....nna I need some help in physics electricity ...just hints how we do what n how to solve some of the problem... just hints
Xiluva
The first thing you can do is to understand ohm's law and the difference between a series and parallel connection concerning current, resistance and potential difference
Thendo
Hi Xiluva,not sure if this will be helpful but to understand electricity better I suggest you download Siyavula physical science books there's both a learner book and a teacher's guide I was struggling too they really did help you might be able to do some exercises after reading siyavula material
LUTHO
what diode mean
Ansiwe
diode s a part of electrical current tht allows only moves to one direction ..only ...
Frank
allows current .....to flow to one direction I meant .
Frank
ok thanks
Ansiwe
ok thanks guys
Xiluva
temperature surface area concentration addition of a catalyst
Joseph
thank you mr
Mzukisi
How to calculate e.p
ep=mgh
mudodzwa
Ep=mgh
Maximurm
What is polymer
chemical compound with molecules bonded together in long ,repeating chains
Bukani
hey guys i need help with the topic of forces and their application
A force is a pull or push and it can be applied in rocket launchers moving cars & stoping (breaking them).
Duncan
A force is that Agency which changes the object's state of rest or motion. A push or pull are the effects of force.
Katiso
are you sure u wantd to ask tht or u wantd to say " how many bonds are there in alkane nd their names?" ?
I also think that's what she meant 'coz I don't really understand her question
LINDOKUHLE
yeah nd if that's th case , there are only single bonds wch I could say one of em tht I know is methane
Frank
I mean methane,ethane they end up to what
Sylvia
well I also assume ths is wah u lookin for .. methane , ethane , propane, butane, pentane, hexane , Heptane, octane , nonane , decane . is ths wah u wanted ?
Frank
how many alkane are there n there names