work and machines what do you think? how can a machine make work easier?
TRANSCRIPT
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Work and Machines
What Do You Think?
How can a machine make work easier?
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Work and Machines
• Work occurs when a force causes an object to move in the direction of the force.
• A machine is defined as something that makes work easier.
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You know when work is done on an object if two things happen:
1. the object moves as a force is applied
2. the direction of the object’s motion is the same as the direction of the force applied.
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• Calculating Work
Work = Force x Distance (W= F x d)
• The unit used to express work is the joule (J).
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• 1. Suppose you lift a 75 n bowling ball 2 m off the floor. How much work do you do?
• 2. How much work is required to lift two 50 N bowling balls 1 m off the floor?
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• Power is the rate at which work is done.
• Power = Work / time
• The unit for power is called a watt.
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Work and Machines
There are 6 types of simple machines that help make
work easier.
1. Lever 4. Screw2. Inclined Plane 5. Pulley3. Wedge 6. Wheel and Axle
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Work and Machines
Vocabulary1. Input force - the amount of force you
must put into the machine.2. Output force - the amount of force you
get out of a machine.3. Fulcrum - the fixed point that acts as a
pivot.4. Load - same as the output force. It is
usually what you are trying to move.
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Work and Machines
Lever
A lever is a simple machine that consists of a bar that pivots at a
fixed point, called a fulcrum.
There are 3 classes of levers.
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Work and Machines
1st Class Lever- The fulcrum is between the input force and the
load.- These levers are used to increase force or
increase distance.- Examples include a seesaw, scissors, and
pliers.
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Where would the fulcrum and the load be in a seesaw?
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Work and Machines
1st Class Lever Examples of class 1 levers
see-saw
hammer's claws
scissors
pliershttp://www.enchantedlearning.com/physics/machines/Levers.shtml
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Work and Machines
2nd Class Levers- The load is between the fulcrum and the input force.- They do not change the direction of the input force,
but they do allow you to apply less force than the force exerted by the load.
- Examples include a wheelbarrow and a nutcracker.
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Where is the fulcrum, input force and load on a wheelbarrow?
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Work and Machines
2nd Class Lever
http://www.enchantedlearning.com/physics/machines/Levers.shtml
Examples
stapler
bottle opener
wheelbarrow
nail clippers
nut cracker
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Work and Machines
3rd Class Levers- The input force is between the fulcrum
and the load.
- They increase the distance through which the output force is exerted.
- Examples of these are baseball bats, your bent arm, and fishing rods.
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Where is the input force, output force, and fulcrum when using a
baseball bat?
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Work and Machines
3rd Class Levers
Item
Number of Class 3 Levers Used
fishing roda single class
3 lever
tweezersTwo class 3
levers
tongsTwo class 3
levershttp://www.enchantedlearning.com/physics/machines/Levers.shtml
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Inclined Planes
- An inclined plane is a simple machine that is a straight, slanted surface.
- Inclined planes use a longer distance to exert a smaller force.
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Work and Machines
Wedge
- A wedge is a double inclined plane that moves.
- Examples include doorstops, ax heads, and knives.
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Work and Machines
Screws
- A screw is an inclined plane wrapped around a cylinder.
- Examples include a screw, jar lid, soda bottle caps
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Work and Machines
Pulleys
A pulley is a machine that consists of a grooved wheel that holds a rope or a cable.
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Work and Machines
Pulleys
- A load is attached to one end of the rope, and an input force is applied to the other end.
- Examples include flagpoles, sailboats, blinds, and curtain rods.
- There are two types of pulleys- fixed and moveable.
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Work and Machines
Fixed Pulleys
- A fixed pulley has been attached to a stationary, or fixed, object.
- Fixed pulleys change the direction of the force, but they do not increase force.
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Work and Machines
You can use fixed pulleys to pull
down on a rope to lift up the object.
Fixed pulleys
http://the-office.com/summerlift/pulleybasics.htm
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Work and Machines
Moveable Pulleys
- Moveable pulleys increases the force without changing the direction of the force.
- The input force must be exerted over a greater distance than load is moved.
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Work and Machines
Moveable Pulleys
The moveable pulley is attached
to the object being moved.
http://the-office.com/summerlift/pulleybasics.htm
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Work and Machines
Wheel and Axle
- A wheel and axle is a simple machine consisting of two circular objects of different sizes.
- The wheel is the bigger circle, while the axle is the smaller of the two.
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Work and Machines
Examples of wheel and axles are doorknobs, wrenches, and steering wheels.
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Work and Machines
• Most machines that we use are compound machines.
• Compound machines are made of two or more simple machines.