Investigate Machines

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# Investigate Machines - PowerPoint PPT Presentation

Investigate Machines. 4D investigate and demonstrate [mechanical advantage and] efficiency of various machines such as levers, motors, wheels and axles, pulleys, and ramps. Work. Work requires that an object must move. Force must be in the direction of the movement.

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Presentation Transcript

### Investigate Machines

4D investigate and demonstrate [mechanical advantage and] efficiency of various machines such as levers, motors, wheels and axles, pulleys, and ramps.

Work

Work requires that an object must move.

Force must be in the direction of the movement.

Work = Force x distance Units: N-m , J (joule)

Machines
• A machine is used to do work and can:
• Change force and distance or direction
• Uses less force but goes a longer distance
• Cannot take less work with a machine
• Takes more work when friction is present
Levers
• Three parts: force, load, and fulcrum
• The greater the distance to the fulcrum the greater the force.
Wheel and Axle
• Wheel and axle or lever attached to a shaft.

Steering wheel

Door knob

Hinge

Smaller force on wheel produces larger force on axle.

Inclined Plane

Work done is the same no matter what the angle.

The shorter ramp requires more effort

but a shorter distance.

More work is done when friction is present.

Screw
• A screw is a spiral inclined plane.
• An inclined plane wrapped around a cylinder.
• Less force required over a longer distance
Wedge
• Double inclined plane
• When you use a wedge you redirect the force.
Machine Calculations

Mechanical advantage measures how much the machine increases your effort force (big MA is better)

Effort Force

= Effort Distance

Resistance Distance

MA = FR = DE

FE DR

Percent Efficiency = W out x 100 %

W in

Power
• Rate at which work is done
• Power = Work P = W

Change in time ∆t

Time = 2s Time = 5s

P = W = 10 J = 5 J/s = 5 W P= 10 J = 2 J /s = 2W

∆t 2s 5s

Units: J/s, Watt (W), Kilowatts (KW)

What is a Simple Machine?
• A simple machine has few or no moving parts.
• Simple machines make work easier
Wheels and Axles
• The wheel and axle are a simple machine
• The axle is a rod that goes through the wheel which allows the wheel to turn
• Gears are a form of wheels and axles
Pulleys
• Pulley are wheels and axles with a groove around the outside
• A pulley needs a rope, chain or belt around the groove to make it do work
Inclined Planes
• An inclined plane is a flat surface that is higher on one end
• Inclined planes make the work of moving things easier
Wedges
• Two inclined planes joined back to back.
• Wedges are used to split things.
Screws
• A screw is an inclined plane wrapped around a shaft or cylinder.
• The inclined plane allows the screw to move itself when rotated.
Levers-First Class
• In a first class lever the fulcrum is in the middle and the load and effort is on either side
• Think of a see-saw
Levers-Second Class
• In a second class lever the fulcrum is at the end, with the load in the middle
• Think of a wheelbarrow
Levers-Third Class
• In a third class lever the fulcrum is again at the end, but the effort is in the middle
• Think of a pair of tweezers
Simple Machines
• Simple Machines can be put together in different ways to make complex machinery

1. The diagram shows an electric motor lifting a 6N block a distance of 3 m. The total amount of electrical energy used by the motor is 30 J. How much energy does the motor convert to heat?

• 9 J
• 12 J
• 18 J
• 21 J
2. Which lever arrangement requires the least effort force to raise a 500 N resistance?
• [Option 1]
• [Option 2]
• [Option 3]
• [Option 4]

[Default]

[MC Any]

[MC All]

3. What is the efficiency of an air conditioner if there is a work input of 320 J and a work output of 80 J?
• 4%
• 25%
• 240%
• 400%

[Default]

[MC Any]

[MC All]

4. Which configuration of pulleys and belts shown below will result in the fastest rotation of Spindle 2?
• [Option 1]
• [Option 2]
• [Option 3]
• [Option 4]

[Default]

[MC Any]

[MC All]

5. Which of these represents a properly balanced system?
• [Option 1]
• [Option 2]
• [Option 3]
• [Option 4]

[Default]

[MC Any]

[MC All]

6. Which lever requires the least effort to lift the load?
• [Option 1]
• [Option 2]
• [Option 3]
• [Option 4]

[Default]

[MC Any]

[MC All]

7. Which of the following explains why the machine shown above has an efficiency of less than 100%?
• The effort force is less than the resistance force.
• The load must be less than the force.
• The load and the force act in opposite directions.
• The motion between the rope and the pulleys produces friction.

[Default]

[MC Any]

[MC All]

8. A person uses a force of 600 N to lift a box from the ground to the top of the ramp shown. Another worker uses a force of 300 N to push the same box up the complete length of the ramp. What is the approximate percent efficiency of the ramp?

• 17%
• 23%
• 77%
• 83%

[Default]

[MC Any]

[MC All]