Scope of the presentation Scope of this presentation is to learn below engineering concepts : Torque and force Work Power Friction and lubrication

Basic Terms - Force 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.”)

Gravity The 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)

Basic Terms - Torque 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 with rotational motors and axles. This motor produces a torque.

Force and Torque How are force and torque related? A force here... …produces a torque 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).

Basic Terms - Work 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 work Understanding the 2 components of Work is the key to understanding mechanical advantage. Question: Where would you hold the wrench for it to be most effective?

Mechanical Advantage 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.

Mechanical Advantage 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.

Mechanical Advantage 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 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

Power If 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 done The more powerful an object the faster it can do work

Power Power is measured in Watts where 1 watt =1j/s If something has a power of 20watts it can do 20j of work in 1 second Why 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 lubrication Friction is the force that prevents easy movement between two objects in contact A 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?