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.