Mechanical SystemsMechanical Systems

Topic 1 - Levers and Inclined PlanesTopic 1 - Levers and Inclined Planes

Lever • A simple machine that changes the amount of force you need to

move an object

Parts of a lever

1. Fulcrum – The fixed point that is the lever’s point of rotation

2. Effort Force – The force you exert on a lever to make it move

3. Load – The mass of an object moved or lifted by the lever

Three Classes of Levers

1. Class 1 Lever – The fulcrum is between the effort and the load

2. Class 2 Lever – The load is between the effort and the fulcrum

3. Class 3 Lever – The effort is between the fulcrum and the load

Examples of Levers

Class 1 Levers – A see – saw, hammer, scissors, pliers, trolley, crowbar

Class 2 Levers – Bottle opener, stapler, wheelbarrow, nail clippers, nutcracker

Class 3 Levers – Fishing rod, tweezers, tongs, hockey stick

What is WorkWhen you exert force on an object to move it in the direction of the force, you are doing work.

Work = Force x Distance• Force is measured in Newtons (1 Newton = approximately 100 grams)• Work is measured in Joules

Example: You exerted a force of 3.5 N on a box and moved it 2 metresW= 3.5 x 2 = 7 Joules

Inclined Planes

An inclined plane is a ramp or a slope that reduces the force you need to lift something.

• Inclined planes and levers reduce the work you do to move an object.

What is Mechanical Advantage The comparison of the size of the load to the size of the effort force. So

the smaller the effort force compared to the load, the greater the mechanical advantage is.

• If you use a machine that requires less effort to move the load, then the greater mechanical advantage the machine has.

• The mechanical advantage tells you how many times easier the simple machine made it to move the object

Calculating Mechanical Advantage

Mechanical Advantage = Load Force/Effort ForceOr

Length of effort Arm / Length of load Arm

Example: 5 Newtons 50 Newtons Mechanical Advantage = 10

15 Newtons 50 Newtons Mechanical Advantage = 3.3

SO...WHICH LEVER MAKES THE JOB EASIER?

Topic 2 – The Wheel and Axle, Gears Topic 2 – The Wheel and Axle, Gears and Pulleysand Pulleys

The Wheel and Axle

Wheels and Axles are also simple machines that provide a mechanical advantage.

Examples:

Gears

A simple machine that consists of a wheel with teeth that is used to reduce work.

Pulleys

A simple machine consisting of a grooved wheel with a rope or chain running through the groove. These are used to make work more convenient and even reduce work.

• Pulleys can be fixed or movable

• Complex pulley systems are used to move very heavy loads

Pulleys and Mechanical AdvantageFixed Pulleys – A fixed pulley does not rise or fall with the load. An

example would be the pulley on top of a flag pole.

• A fixed pulley changes the direction of force but does not create a mechanical advantage. Only you are supporting the weight.

Moveable Pulleys – These rise and fall with the load. • A moveable pulley does not change the direction of force, but it does

have a mechanical advantage. It creates a mechanical advantage because now the weight is being supported where the rope is attached and by you (supported in two areas). The mechanical advantage is = to the number of ends of the rope supporting the weight.

• So the moveable pulley would have a mechanical advantage of 2.

Speed Ratio = Distanceinput÷ Distanceoutput

The more teeth a gear has, the slower it turns in a speed train. Smaller gears with fewer teeth move faster.

Speed ratio is the relationship between the speed of the driver gear and a follower gear.

Speed ratio = # of driver gear teeth

# of follower gear teeth

Here is a pulley design with a mechanical advantage of two

Here is a pulley design with a mechanical advantage of three

Topic 3 – Energy, Friction and EfficiencyTopic 3 – Energy, Friction and Efficiency

Stored Energy

• Energy must be transferred to a machine to make it work, however, we need to store energy to make the machine work only when we want it.

• Stored energy is called potential energy.• Much of the energy for machines as well as our bodies is stored as chemical

energy.

No Machine is 100% Efficient• No machine is perfectly efficient, some energy is always lost .• The more efficient a machine is, the more energy is transferred to the load.

Boosting Efficiency

• Some effort put into any machine must overcome friction.• Friction reduces the efficiency of a machine.• We can boost efficiency by reducing friction. We can reduce friction

by using lubricants.

Useful Friction• Often we need friction to make a machine work properly.• Some examples of this are:

We need some friction on our vehicle tires to make them grip and move

Baseball players add powder to their hands to increase friction and improve grip

Running shoes need friction to provide grip so you don’t slip

Topic 4 – Force, Pressure and AreaTopic 4 – Force, Pressure and Area

Force acting over a certain area is called pressure. When you change the area and keep the force constant, the pressure changes.

Calculating PressurePressure = Force / Area• Force is measured in Newtons and area in square meters

Pressure is measured in Newtons/m2.

Example – If there is a force of 10N spread over 10 square meters. The pressure would equal 1 Newton/m2. If the same force was spread over 1 square meter then the pressure would be 10 Newtons/m2. The second would have greater pressure.

• Pressure increases when there is more force over less area. If you kept the force the same and increased the area over which the force was applied, the pressure would decrease.

An example of this is the man laying on a bed of nails:

• If he has a force of 800 Newtons laying on 4 square meters, the pressure pushing on his back is 200 Newtons/m2.

• If he stood on his feet and put his 800 Newtons on .5 square meters, the pressure pushing on his feet would be 1600 Newtons/m2...much more pressure.

Pascal’s LawThis law states that pressure exerted on a contained fluid is transmitted

undiminished in all directions throughout the fluid and perpendicular to the walls of the container.

Mechanical systems use this law. An example would be in using hydraulic lifts. Pressure is applied to a hydraulic arm, and this pressure is used to cause the lift to do work.