Topic 2.1 – Machines Make Work Easier Mechanical Systems

Making work Easy! Think of a road going up a mountain. Does the road go straight up the mountain? If not, how does it work? Is this a simple machine?

Mechanical Advantage The mechanical advantage of a machine is the amount by which a machine can multiply a force MA = OF IF

Speed Ratio Speed measures the distance an object travels in a given amount of time. Speed Ratio is a measure of how the speed of an object is affected by a machine.

Formula The formula for calculating the speed ratio is: Speed Ratio = Input Distance Output Distance

Example Calculate the speed ratio: Input distance = 4m Output distance = 1m Speed Ratio = 4m 1m = 4

Calculate the mechanical advantage: Input force = 45N Output force = 180N MA = 180N 45N = 4

Speed Ratio = ???? Mechanical Advantage = ???

Why are the answers the same? Did you notice that the Mechanical Advantage and the Speed Ratio’s you calculated are EXACTLY THE SAME? What is one thing we talked about that would impact the mechanical advantage of an inclined plane? HINT: it starts with an “F”

Friction Both the mechanical advantage and the speed ratio are the same in these calculations but in reality this would not be the case because of friction. Friction is a force that opposes motion caused by the surface roughness of materials.

A rough surface creates more friction than a smooth surface…. Soooo… The mechanical advantage will be impacted due to friction depending on the type of surface. Think about pushing a box up a ramp. The box rubbing on the ramp would make you have to push harder in order to get that box to the top. THIS IS FRICTION!

Ideal Mechanical Advantage Speed ratio is the IDEAL MECHANICAL ADVANTAGE because it is not affected by friction since it is calculating the distance that an object has to travel.

Efficiency No machine is 100% efficient! Efficiency is the measure of how well a machine uses energy

Formula for Efficiency Efficiency = mechanical advantage x 100 Speed Ratio We multiply by 100 because we want a percent!

Example a pulley has a speed ratio of 3 and a mechanical advantage of 2 what is its efficiency?

Inefficient! complex machines are often very inefficient because of the many subsystems that are each affected by friction – FOR EXAMPLE:   a car engine usually has an efficiency of about 15% meaning that 85% of the energy from the gas is not used to move the car most of it ends up as heAT