Unit 5 - Mechanical Systems Notes1. Simple Machines:

Lever: A simple machine that changes the amount of force you need to put on an object to move that object.

• It consists of a bar that rotates around a fixed point, the fulcrum.

• Effort force: The force you exert on a lever to make it move.• Load: The mass of an object that is moved or lifted by a

machine such as a lever.• Effort arm: The distance between the fulcrum and the

effort force.• Load arm: The distance between the fulcrum and the load.

Type of Lever Description Example DiagramFirst Class The fulcrum is between the effort and

the load.Scissors

Second Class The load is between the effort and the fulcrum. Always exerts a greater force on the load than the effort force you exert on the lever.

Wheelbarrow

Third Class The effort is exerted between the fulcrum and the load. You must put greater force on the lever than the lever exerts on the load. However, the load can be moved very quickly.

Hockey stick

Inclined Plane: A ramp or a slope that reduces the force you need to exert to lift something.

Wheel and Axle : Two turning objects are attached to each other at their centers, and one causes the other to turn. Winch: Consists of a small cylinder and a crank or handle. (A wheel-axle device)

• Radius = The distance from the centre of the wheel to the circumference. The radius acts like the load arm of a lever.

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Gear: A rotating wheel-like object with teeth around its rim.• Gear Train: A group of two or more gears• Driving Gear: First gear, the one in which the initial force is

applied. • Driven Gear: Second gear, the one that gets driven• Look at the diagram to the right… Which is the Driving gear?

Which is the Driven gear?• Sprocket: A gear with teeth that fit into a chain, like on your bike.

Pulley : A grooved wheel with a rope or chain running along the groove.

Fixed pulley: A pulley that is attached to something that does

not move.

Movable pulley: A pulley that is attached to something else,

often by a rope that goes around the pulley itself.

Compound Pulley: Several pulleys working together.

2. Simple Machines Calculations:

How to complete a Simple Machines Calculation (and other Physics Calculations!):

1) List the values that are known and the unknown value. The unknown value is what you are solving for.

2) Decide which form of the given equation to use (the one that will let you solve for the unknown). Use the triangle to help you with this.

3) Place the given values into the equation.4) Calculate. Make sure to write down the correct units in your answer!

Symbols/Units that we will use for our Simple Machine Calculations:

Name: Work Force Distance Mechanical Advantage

Load Force

Effort Force

Efficiency

Speed Ratio

Symbol: W F D MA FL FE Eff SRUnit: Joules Newtons meters no unit Newtons Newtons percent no unitUnit

symbol:J N m N N %

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Calculating Work (W):

Work is energy in action. It is defined as the product of the force exerted times the distance moved.

W= Force(N) x Distance(m)

Examples:1. A wheelbarrow with a weight of 100 N is pushed 5 m. How much work is accomplished?

2. If a crane does 4000 J of work lifting a load of 400 N, how far is the load lifted?

Questions:1. Carlos does a chin-up in gym class and raises himself 0.8 m. If Carlos has a weight of 620 N, how

much work does he accomplish? (496 J)

2. A game show contestant won a prize by pushing a bowling ball 20 m using her nose. The amount of work done was 1470 J. How much force did the contestant exert on the ball? (73.5 N)

3. Carla does 2300 J of work while running 2000m. How much force did she need to push herself that distance? (1.15 N)

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Calculating Mechanical Advantage (MA):Mechanical Advantage is the comparison of the force

produced by a machine to the force applied to a machine. It compares the size of the load force to the effort force. The

work you do on a machine is called input force/effort force. The work the machine does on the load is called

output force/load force.

MA = Load Force (FL) Effort Force (FE)

Examples:

1. What is the mechanical advantage of a lever that lifts a load of 24 N with an effort of 20 N?

2. If a simple machine has a mechanical advantage of 3, what input force is required to lift a load of 9 N?

Questions:

1. A machine uses an input force of 200 N (newtons) to produce an output force of 800 N. What is the mechanical advantage of this machine?(4)

2. A machine is designed to lift an object with a weight of 12 N. If the input force for the machine is set at 4 N, what is the mechanical advantage of the machine? (3)

3. A machine is required to produce an output force of 600 N. If the machine has an input force of 100 N, what is the mechanical advantage? (6)

4. A machine with a mechanical advantage of 10 is used to produce an load force of 250 N. What effort force is applied to this machine? (25 N)

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5. An input force of 35 N is applied to a machine with a mechanical advantage of 0.75. What is the size of the load this machine could lift (how large is the output force)? (26.25 N)

Calculating Speed Ratio (SR):

The relationship between the speed of rotations of a smaller gear and a larger gear is called the

speed ratio.

SR = # Driven Gear Teeth # Follower Gear Teeth

Examples:

1. In a gear system, a driven gear has 15 teeth while a follower gear has 5. What is the speed ratio?

Questions:

Bobby has just gotten a new 20-speed bike from his mom for his birthday. There are 2 gears on the front and 10 gears on the back. Write the following table in your notebook and fill in the blank column for Speed Ratio for each of his gears.

# Teeth on Back Gears of Bobby’s

Bike

# of Teeth on Front Gears of Bobby’s Bike

36 50

12

13

14

15

16

17

19

21

23

5

25

Calculating Efficiency (Eff):Machines convert one form of energy into

another. An ideal machine would transfer all of its energy, but in real machines energy is always

lost. The efficiency of a machine can tell you how much energy is being lost. Efficiency is

usually stated as a percentage.

Eff = Work done by Machine on Load x 100 Work done on Machine by Effort

Example:

1. A lever uses 45 J of input from a person to complete 40 J of work on a load. What is its efficiency?

Questions:

1. A lever is required to lift a box using 115 J of input energy. The work done on the load is 103 J. What is the efficiency of the lever? (89.6%)

2. (Challenge) A machine moves a crate that weighs 100 N up to a height of 3 m. The input work that the machine requires is 450 J. What is the efficiency of the machine? (66.7%)

3. (Challenge) A machine with an efficiency of 73% does 400 J of work on a load. What is the effort work required? (548 J)

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3. Force, Pressure and Area:

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