Simple Machines As well as Work Efficiency and

Simple Machines As well as Work Efficiency and Mechanical advantage

What is a machine? A machine may be thought of as a device that makes work easier.

How do machines make work easier? Machines make work easier by: multiplying the size of the force you exert (such as in this pulley system).

Machines also make work easier by: changing the direction of that force (such as in the gear, roller & rope assembly in these mini-blinds) A pulley lifting a mass or a pulley on a flagpole.

A machine can also do both: multiplying the amount of the force, as well as changing the direction of the force. (such as this pry bar)

Other things machines do: Machines transfer force from one place to another. Example: A bicycle chain transfers force to the pedals Machines can convert energy from one form to another. Example: This electric generator converts chemical energy (gasoline) to mechanical energy to electrical energy. – Not a simple machine.

Machines can multiply speed or distance. During one revolution of the bicycle’s pedals, the rim of the wheel travels faster than the pedals.

What are simple machines? A Simple Machine is a device that does work with one movement. Simple machines overcome gravity and friction. Pry bar used to prying up a rock against gravity

When you use a pry bar to remove a lid, you are working against friction----the friction between the nails in the lid and the crate. • When using a simple machine, you are trying to move something that resists being moved.

Applying Force & Doing Work • Two forces are involved when a machine is used to do work. First: Effort force (Fe ) – the force applied to the machine Second: Resistance force (Fr) –the force applied by the machine to overcome resistance.

• The pry bar is used to multiply the effort force and open the crate. However, to gain force the effort must push through a greater effort distance than the resistance distance.

Law of Work and the Ideal Machine • In an “Ideal Machine” is frictionless --therefore there is no energy loss from friction and heat. • For an ideal machine, the work input is equal to the work output. • This is called the “Law of Work. ”

Ideal Machines Equation

So in order that work input equals work output, the effort force must travel a greater distance than the resistance force.

Law of Work Calculation -Ideal Machines • A 500 N barrel is rolled up a 4. 00 m ramp to a platform 1. 20 m above the ground. What force must be applied to the barrel.

How much force would be used to lift the barrel to then platform without a ramp? Since the barrel has a weight of 500 N, the effort force required to lift the barrel would be 500 N. The work done on the barrel would be W = Fd (500 N x 1. 20 m = 600 N).

THE MECHANICAL ADVANTAGE: The Number of times a machine multiplies the effort force is the Mechanical Advantage (MA) of the machine.

Mechanical Advantage Calculation – for Ideal Machines • For the barrel-ramp problem: The ramp, therefore multiplies the effort put in to moving the barrel to the platform over three times.

What about a less than ideal machine? • In the real world, friction acts against a machine’s work output, whether it is a pulley system or a ramp. The less friction the more efficient the machine, and the greater the work output.

Machine Efficiency Calculation

Sample Calculation • A sofa weighing 1500 N must be placed in a truck bed 1. 0 m off the ground. A mover uses a force of 500 N to push the sofa up an inclined plane that has a slope length of 4. 0 m. What is the efficiency of this inclined plane?