Machines and Mechanical Advantage

What is a machine? What can it do? Transform type of energy Deliver energy Increase force Increase speed Change direction of force Reduce friction In general: they help

Benefits of machines: mechanical advantage Think of something very basic: a bottle opener. If you want to open a bottle, you could try to lift the cap with the force from your fingers. or you could apply that force to a bottle opener which then transfers the force to the cap Much easier…but why?

Mechanical advantage The force you exert on the machine (the bottle opener) is called the effort force The force exerted by the machine is called the resistance force They are not necessarily the same The resistance force could be greater but machine can’t do more work than you put in So if the work can’t grow but the force can, what must change?

If work is the same, decreased force means increased distance. In other words, we put in less force but over a greater distance

Calculating Mechanical Advantage Mechanical advantage is the resistance force divided by the effort force. In other words, the force you get out over the force you put in If you put in a little force and get out a larger force, you will have a >1 MA MA=Fr/Fe

Calculating MA Back to the opener: If you exert a force of 2N on the bottle opener and it exerts a force of 4N on the cap: MA=Fr/Fe=4/2=2 This is good- MA of >1 means it is decreasing the force you have to put in- you are gaining mechanical advantage

Not all machines increase the force Can you think of an example where you put in more force and get out less? In this case you probably don’t need much force but you could get that force over a greater distance This can also be used to increase speed- now can you think of other examples like this?

We use these machines to increase speed (move it through more distance)

As we just saw, sometimes we are not after a mechanical advantage In fact, some machines keep the force the same but change the direction of force to make life easier on us This pulley lets him pull down instead of lifting up- the change in direction helps him even without any MA Changing direction