Scope of the presentationScope of this presentation is to learn below

engineering concepts :

Torque and force Work Power Friction and lubrication

What is a “force?”

A force causes something with mass to move (accelerate).

This can be summed up with Newton’s 2nd Law. F = m x a

Question: What force do we experience every single day?

Answer: The force of gravity.

(In fact, units of force are called “Newtons.”)

GravityThe strength of gravity between two

objects depends on two factors:1. Masses of the objects (If mass

increases, force also increases)2. Distance between the objects (If

distance increases, force decreases)

What is “torque?”

Torque can be thought of as rotational force.

Torque causes something with mass to rotate.

We are interested in “torque” because we deal withrotational motors and axles.

This motor produces a torque.

How are force and torque related?

A force here...…produces atorque here.

moment arm.

A force can create a torque by acting through a moment arm.

The relationship is = F x r. r is the length of the moment arm (in this case, the length of the wrench).

Work (in physics) is defined as a force acting over a distance.

W = F x d

Work in terms of rotation is a torque acting over an angle.

W = x

Understanding the 2 components of Work is the key tounderstanding mechanical advantage.

Question: Where would you hold the wrench for it to be most effective?

If you hold the wrench here, you need a lot of force...

If you hold the wrench here, you don’t need as much force...

You will not be able to move very far. …Your hand moves a

long way.

It takes the same amount of work to turn the bolt.

You can opt for a lot of force and little distance.W = F x d

Or you can choose a little force but a lot of distance.W = f x D

In many of our machines, we want to increase our force, so we don’t mind going the extra distance.

Question: Which ramp would you prefer to use to move a heavy weight to the top of the box?

Answer: This ramp requires less force, but you have to move the weight a longer distance.

Power is the rate at which work is done. It can be thought of as work per second.

Power = Work / sec.

Which of these machines would you prefer to use to cool you down on a hot day?

Fan Works on 230 V AC

Battery operated fan

PowerIf you said the first one it is probably because

you know it would cool you down more because it is more powerful than the battery operated fan

Power is the rate at which work is doneThe more powerful an object the faster it can

do work

PowerPower is measured in Watts where 1 watt =1j/sIf something has a power of 20watts it can do

20j of work in 1 secondWhy do you think a 60w bulb is brighter than a

10w bulb?We can work out power by dividing work done

by the time taken to do the work Power (w) = Work done (j) Time (s)

Friction and lubricationFriction is the force that prevents easy movement

between two objects in contactA LUBRICANT is anything that reduces friction

High friction : Sand paper, Car Tyres and rough soled shoes

Low Friction: wet soap, ice and glass

What would you use to reduce friction in the chain of your bicycle ?If you said oil you are correct!

Oil is an example of a LUBRICANT

Can you think of any others?

To investigate friction

Using a force sensor, a water bottle, piece of carpet or mat and some oil how can we show the effect of friction and lubricants?

Why .... ?

Why you can get a burning feeling? this is because friction causes heat

Why do you think swimmers, skiers and cyclists all shave their legs?