Machines make work easier 2 1 Mechanical Advantage

Machines make work easier. 2. 1

Mechanical Advantage ¨ - A winding road is actually a series of inclined planes with switchbacks, which allow cars to drive up a steep hill. ¨ Mechanical Advantage – amount by which a machine can multiply a force. (or how much the machine does the work to move an object) – also called the force ratio

Mechanical Advantage Definitions: ¨ Input Force – force applied to the machine. ¨ Output Force – force the machine applies to the object. – Force is measured in Newtons (N). – (1 kg = 9. 81 N of force) Mechanical Advantage= Force output (N) Force Input (N)

Mechanical Advantage ¨ MA > 1 = applied force is bigger than resulting force – Most simple machines work like this ¨ MA = 1 = No advantage (both sides give equal amounts of force) ¨ MA< 1 = resulting force is less than the applied force – Doesn’t necessarily mean the machine is flawed, but serves a different purpose – Ex. Screws have low MA. If if had a high MA, it would

A Mechanical Advantage Less Than 1 ¨ Useful for tasks that do not require a large output force. – Ex) Bicycle – the output force is used for speed. – MA greater than one requires more work • Ex. Pulleys, or pulling a rope has a MA of 2.

¨ 1. Calculate the mechanical advantage for a lever that has the following characteristics: (2 marks) ¨ Input force: 200 N ¨ Output force: 550 N

Mechanical Advantage Questions Bill Nye – Mechanical Advantage

Speed ¨ Speed – measures the distance an object travels in a given amount of time. Speed= Distance (m) Time(s)

¨ 1) Calculate the speed of a person running the 400 m race in 55 seconds

Speed Ratio ¨ Speed Ratio – measure of how the speed of the object is affected by a machine. – SR describes how much faster the user is moving than the load is working (or how much effort you need to put into it to get out of it) SR= Input Distance (m) Output Distance (m)

¨ 1. Calculate the speed ratio for a lever that has the following characteristics: (2 marks) ¨· Input distance: 45 m ¨· Output distance: 15 m

Speed Ratio Questions

Recall ¨ ** A machine can increase or change the direction of the force that you apply. ¨ But, the cost is that the force the user applies must move farther than the load.

The Effect of Friction ¨ Friction – force that opposes motion. ¨ - caused by the roughness of surfaces. ¨ - As roughness of a surface increases so does the effect of friction. ¨ Mechanical Advantage does NOT always equal Speed Ratio. ¨ - Friction can affect MA, but not SR. ¨ - Speed ratio represents the ideal mechanical advantage (No friction).

Efficiency ¨ - Friction creates HEAT, and must be released to protect the system. ¨ ¨ Efficiency – measurement of how well a machine or device uses energy. – affected by friction. – most energy lost is unusable (ex. Heat).

Efficiency= MA SR OR Output Energy Input Energy Most complex machines are very inefficient: waste energy. – Ex) Car – 15% efficient.

¨ 1. Calculate the efficiency for a lever that has the following characteristics: (4 marks) ¨· Input distance: 45 m ¨· Output distance: 15 m ¨· Input force: 200 N • Output force: 550 N

¨ MA= Output force/Input force – =550 N/200 N – = 2. 75 ¨ SR= Input distance/Output distance – = 45 m/15 m – =3 ¨ E= MA/SR – = 2. 75/3 – =0. 9166 – =91. 7%

¨ Efficiency Questions

Formulas to know thus far: MA= Output force/Input force S=Distance/Time (m/s) SR= Input distance/ output distance Efficiency= MA/SR

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Homework! ¨ C & R p. 286 ¨ 2 -5 ¨ Practice Questions