1. Work and Simple Machines

2. What is Work?
In science, work includes forces and motion but not concentration.
Work
The transfer of energy that occurs when a force is applied over a distance
Work is done when you apply force
Unit of measurement for work is joules (J)
Calculating work
Can be easily done
Formula:
W= Fd
W: work (joules)
F: force (Newtons)

3. What is Work?: Factors that Affect Work
The work done on an object depends on the direction of the force applied and the direction of motion.
Force at an Angle:
The force and motion aren’t in the same direction
Only part of the force does work
Example:
Suitcase
The force will be both horizontal and vertical
Only the horizontal force moves the suitcase, and, therefore, it’s the only force that is calculated when calculating work
Lifting Objects:
Example:
Lifting a backpack requires work.
Has weight because of gravity pushing down on it
Must pull upward with a force that is greater than or equal to the backpack’s weight
The work done to lift any object is equal to the weight of the object multiplied by the distance it is lifted

4. What is Work?

5. What is Work? Work and Energy
Doing work on an object transfers energy to the object
Helps in predicting how an object will act when forces are applied to it
Kinetic energy
Energy that causes an object to move
Potential energy
Energy at a stand still
Example:
Lifting an object
Increases the object’s energy

6. What is Power? Doing work does affect power Power
The rate at which work is done
Unit of measurement for power is Watt (W)
Calculating power
Formula:
P=work/time
W: work (joules)
T: time (seconds)

7. What is a Machine?
A machine is any device that makes doing work easier.
Can range from simple to complex
Simple:
Snow shovel
Complex:
Watch
All machines make tasks easier, but they don’t decrease the amount of work required.
Instead, a machine changes the way in which the work is done.

8. What is a Machine? Input Force to Output Force
Input Work to Output Work
Input force
The force that you apply to an object
Output force
The force that the object changes the input force into and puts out
Input work
Occurs when you apply an input force to a part of the machine
Result of the input force and the distance the machine moves in the direction of the input force
Output work
Converted from input work
Occurs when a machine applies the output force on something and making it move
The result of the output force and the distance part of the machine moves in the direction of the output force

9. How do Machines Make Work Easier to Do?
Makes work easier three ways by changing the following:
The size of a force
The distance the force acts
The direction of a force

10. How Do Machines Make Work Easier to Do?
Change in the Size of a Force
Change the Distance the Force Acts
Occurs when the output force is greater than the input force, the output force acts over a shorter distance
In other words, a machine makes the work easier by changing the input force into a larger output force
Occurs when the output force acts over a longer distance than the input force, the output force is less than the input force
In other words, the output force decreases as the distance over which the force acts increases

11. How Do Machines Make Work Easier to Do?
Change the Direction of a Force
Equal output and input forces act over equal distances
In other words, when the output and input forces are equal, then it can change the direction of the force.

12. What is Mechanical Advantage?
Most machines change the size of the force applied to them.
Mechanical advantage
The ratio of a machine’s output force produced by the input force applied
Tells how many times larger or smaller the output force is than the input force
Can be:
Less than 1
Equal to 1
Greater than 1
Ideal mechanical advantage can occur if no friction existed
Machines can’t operate at ideal mechanical advantage because friction does exist

13. What is Efficiency?
The output work done by a machine never exceeds the input work of the machine
Reason is because of friction
Friction converts some input work into thermal energy, which can’t be used to do work
Efficiency
The ratio of a output work to the input work
A machine’s efficiency is always less than 100% because the output work is always less than the input work
Example:
Lubricating a machine’s moving parts increases the efficiency

14. What is a Simple Machine?
A machine that does work using only one movement
Six types of Simple Machines:
Levers
Wheel and axle
Inclined plane
Wedges
Screws
Pulleys

15. Levers
Lever
A simple machine made up of a bar that pivots or rotates about a fixed point
The fixed point is called the fulcrum
In levers, the distance from the input force to the fulcrum is known as the input arm
In levers, the distance from the fulcrum to output force is known as the output arm
Three types of levers:
First-class lever
Second-class lever
Third-class lever

16. First-Class Levers
The fulcrum is between the input force and output force
Mechanical advantage for these levers depends on the location of the fulcrum.
Greater than 1
The input arm is longer than the output arm
Equal to 1
The input and output arms and input and output forces are equal
Less than 1
The input arm is shorter than the output arm
Examples:
Hammer
Finger tab on a beverage can

17. Second-Class Levers
The output force is between the input force and fulcrum
The output force and input force act in the same direction
Makes the output force greater than the input force
Mechanical advantage:
The input arms are longer than the output arms, causing the mechanical advantage to always be greater than 1.
Examples:
Wheelbarrow
A nut cracker
Your foot

18. Third-Class Levers
The input force is between the output force and the fulcrum
The output force is less than the input force
Both forces act in the same direction
Mechanical Advantage:
The input arm is always shorter than the output arm, making the mechanical advantage lesser than 1
Examples:
Tweezers
Rakes
Broom

19. Types of Levers

20. Levers in the Human Body
The human body uses all three classes of levers
Examples:
Neck
First-class lever
Fulcrum is the joint connecting the skull to the spine
Neck muscles provide input force, and output force helps to support the head’s weight
Foot
Second-class lever
Ball of the foot is the fulcrum
Input force comes from the muscles in the calves
Arm
Third-class lever
Elbow is the fulcrum
Input forces comes from the muscles located near the elbow

21. Wheel and axle
An axle attached to the center of the wheel and both rotate together
Axle can be another word for shaft
Example:
Screwdriver
Steering wheel in a car
Mechanical advantage
The length of the input arm is the radius of the wheel
The length of the output arms is the radius of the axle
Help in showing ideal mechanical advantage
Mechanical advantage is usually greater than 1 because of the wheel being larger than the axle

22. Wheel and Axle

23. Inclined planes A flat, sloped surface
Also called a ramp
Takes less force using an inclined plane than it does to lift an object straight up
Helped the Egyptians in building the pyramids
Examples:
Wheelchair ramps
Ramps used by moving trucks

24. Wedges A sloped surface that moves
A type of inclined plane with one or two sloping sides
The shape of a wedge gives the output forces different directions than the input forces
Examples:
Doorstop
Axe
Teeth

25. Screws An inclined plane wrapped around a cylinder
When turning a screw, the screw threads change the input force to an output force
The output force is what pulls the screw into the material

26. Pulleys
A simple machine that is a grooved wheel with a rope or a cable wrapped around it
Can be found in construction sites on the cranes
helps to lift heavy loads
Fixed pulleys
Pulleys that are mounted
Only changes the direction of the force
Example:
Window blinds

27. Pulleys Moveable pulleys Pulley system Mechanical advantage of pulleys
A pulley that can be attached to the object being lifted
Decrease the force needed to lift an object
Distance over which the force acts increases
Pulley system
A combination of fixed and moveable pulleys that work together
Mechanical advantage of pulleys
The ideal mechanical advantage of a pulley and pulley system is equal to the number of sections of rope pulling up on the object

28. Pulleys

29. What is a Compound Machine?
Two or more machines that operate together is a compound machine
Gears
Wheel and axle with teeth
Two or more gears working together form a compound machine
Different sizes helps in turning a different speeds
Smaller gears will rotate faster than larger gears
The amount of force transmitted through a set of gears is also affected by their size
The input force applied to a larger gear can be reduced when applied to a smaller gear
Other examples of Compound Machines:
Can opener

30. What is a Compound Machine?
Efficiency of Compound Machines:
The efficiency is calculated by multiplying the efficiencies of each simply machine together
Each simple machine can decrease the overall efficiency of a compound machine