Checking Concepts
Is work being done if I am holding an object?
no
What type of machine is a wheel barrow?
lever or wheel and axle
work = force x distance
What is the equation for power?
power = work / time
What is the mechanical advantage of a machine that changes only the direction of the applied force?
1
Is a rolling ball doing work?
yes
What type of machine is a ramp?
inclined plane
A tow truck exerts a force of 11,000N to pull a car out of a ditch. It move the car a distance of 5 m. What is the work being done?
55,000 J or 55 kJ
what is the equation for efficiency?
efficiency = output work / input work x 100%
How is calculating the IMA of an inclined plane similar to calculating that of a screw?
both include the length of the incline divided by the height or length.
If I am pushing on a tree for 5 minutes, am I doing any work?
no
How does a pulley work?
It changes the direction of force via additions of rope sections
What is the relationship between work and power?
power is the amount of time work is done.
Your laundry basket weighs 22 N and your room is 3.0 m above you on the second floor. It takes you 6.0 secs to carry the laundry basket up. What is your power?
11 W
Describe the relationship between friction and the efficiency of a machine.
the less friction a machine has the more efficient
Is kicking a ball work?
yes
Illustrate a lever in your body. Include input force, output force, and fulcrum
Ex. elbow is fulcrum, bicep input force, hand up is output force
What part of force: lifting, directional, or horizontal force is work being done?
horizontal
The input work you do on a can opener is 12 J. The output work the can opener does is 6 J. What is the efficiency of the can opener?
50%
How is a real machine like an ideal machine, and how is it different?
real machines and ideal machines both make work easier by decreasing input force
Different because ideal machines have little to no friction force acting upon them.
Is kicking a ball straight up work? Explain
no, the ball is not moving any horizontal distance
If you distribute the incline over a larger distance you are increasing the mechanical advantage.
the object must move partially in the direction the force is applied.
A machine with 60% efficiency does 3,000 J of work. Using the machine, how much work did you do?
5,000 J
Can you consider your thumb a lever? WHy or why not?
Yes, the muscles in your hand provide input force and the output force is used to move your thumb.