Work and Power
What two things do you need to know in order to determine how much work is being done?
Force and distance
How does using a ramp make work easier?
It decrease the force you must apply while increasing the distance over which you apply that force.
Name an example of an inclined plane.
Answers may vary.
What is a fulcrum?
The fixed point a lever pivots around
What are the three main types of pulleys?
Fixed, movable, and block and tackle
Why does running 5 miles take more power than walking 5 miles?
While they both take the same amount of work, running 5 miles takes less time.
What is the difference between input force and output force?
Input force is the force that you apply to the machine while output force is the force that the machine applies on an object.
Name an example of a wedge.
Answers may vary.
What class lever is a wheelbarrow?
Second class
How does a pulley with a single fixed wheel make work easier?
It changes the direction of the force you have to apply so that you are at least pulling with gravity.
How can you tell if work is being done on an object?
If the object moves in the same direction that the force is applied
What are the three ways that machines make work easier?
By changing the amount of force you exert, the distance over which you exert your force, or the direction in which you exert the force
You are being asked to build a ramp that will be used to move objects to a heigh of five feet. How could you increase your ramp's mechanical advantage?
Make a longer ramp
What class lever are a pair of scissors?
First class
How can you increase the mechanical advantage of a pulley system?
By adding more wheels
You hike 5 miles with a 120 Newton pack while your friend hikes 10 miles with a 60 Newton pack. Which of you will have done more work?
Neither, you both did 600 Joules of work.
If you apply 10 Joules of force to a can opener and the can opener applies 2 Joules of force to the can, how efficient is your can opener?
20% efficient
Why do sharper knives have a greater mechanical advantage than dull ones?
The width of the blade is thinner.
What class lever is a stapler?
Third class
How do screwdrivers make work easier?
By decreasing the amount of force you need to apply while increasing the distance over which you apply the force
A crane does 60,000 Joules of work in 30 seconds. How powerful is the crane?
2000 Watts
Why can efficiency never be 100%?
Because some of the input work is use to overcome the force of friction
Why do screws hold two pieces of wood in place better than nails?
They increase the distance over which the force is exerted on the wood.
If you want to increase the mechanical advantage of your lever, what could you do to your input force?
Apply it further away from the fulcrum
A screwdriver has a handle radius of 1 cm and a shaft radius of .2 cm. What is the mechanical advantage of the screwdriver?
5