View
217
Download
2
Category
Tags:
Preview:
Citation preview
Work and Machines
What Do You Think?
How can a machine make work easier?
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.
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.
• Calculating Work
Work = Force x Distance (W= F x d)
• The unit used to express work is the joule (J).
• 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?
• Power is the rate at which work is done.
• Power = Work / time
• The unit for power is called a watt.
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
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.
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.
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.
Where would the fulcrum and the load be in a seesaw?
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
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.
Where is the fulcrum, input force and load on a wheelbarrow?
Work and Machines
2nd Class Lever
http://www.enchantedlearning.com/physics/machines/Levers.shtml
Examples
stapler
bottle opener
wheelbarrow
nail clippers
nut cracker
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.
Where is the input force, output force, and fulcrum when using a
baseball bat?
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
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.
Work and Machines
Wedge
- A wedge is a double inclined plane that moves.
- Examples include doorstops, ax heads, and knives.
Work and Machines
Screws
- A screw is an inclined plane wrapped around a cylinder.
- Examples include a screw, jar lid, soda bottle caps
Work and Machines
Pulleys
A pulley is a machine that consists of a grooved wheel that holds a rope or a cable.
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.
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.
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
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.
Work and Machines
Moveable Pulleys
The moveable pulley is attached
to the object being moved.
http://the-office.com/summerlift/pulleybasics.htm
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.
Work and Machines
Examples of wheel and axles are doorknobs, wrenches, and steering wheels.
Work and Machines
• Most machines that we use are compound machines.
• Compound machines are made of two or more simple machines.
Recommended