simple machines, Work 6.1, 6.2 & 6.3
Simple machines make work easier by increasing what?
The distance over which work has been done.
Describe the circumstances for which the output work would equal the input work in a machine?
The machine would have to be an ideal machine in which there was no friction.
What is eficeincy?
is the measure of work put into a machine is changed into useful output work by the machine
So more input work is changed to?
useful output work.
How is energy transfered?
ENERGY is always transferred from the object that is DOING WORK to the one that has it WORK DONE.
Name one machine that you used in the past week. How did this machine make doing work easier for you?
Electric toothbrush Made brushing my teeth faster
What is energy?
Energy is the ability to do work.
Explain how the scientific definition of work is different from the everyday meaning.
Everyday: anything that involves effort Scientific: same direction as the applied force
Give an example of an machine.
Example: Knives, scissors, door knobs
Find the force needed to lift a 2,000 N weight using a machine with a mechanical advantage of 15.
F(in) = F (out)/MA 133 N
What is the formula?
FORMULA: Work(W)= Force (F)x Distance (D)
Infer how lubricating a machine affects the output force exerted by the machine.
Friction is a force that opposes the motion of two surfaces sliding past each other. Lubrication a machine increases the output force because it decreases friction.
When is there no work?
If the direction of applied force and direction of motion match the work is done. If they don't match the work is NOT being done.
Describe the circumstances for which the output work would equal the input work in a machine.
If there is no friction
Explain why in a real machine the output work is always less than the input work.
In a real machine, some of the input work is converted into thermal energy by friction.
What is a machine?
Is a device that makes work easier Machines can be simple
Infer how lubricating a machine affects the output force (& work) exerted by the machine.
Reduces friction greater output
Why is the output work always less than the input work for a real machine?
Some of the input work is converted to thermal energy by friction
The mechanical advantage of a machine is less than one. Compare the distances over which the input and output forces are applied.
The distance over which the output force is applied is greater than the distance that the input force is applied.
What is an output?
The force applied by the machine is called the OUTPUT
What is an input?
The force that is applied is called the INPUT
Explain why, in a real machine, output work is always less than input work.
The output work is always less because of thermal energy which create friction. The friction slows down the work and that is why the input is more than the output.
fulcrum
the set point on a lever
ONE Joule= ?
One Newton Meter
How do machines make work easier?
1. Machines can make work easier by increasing the distance over which the force is applied. 2. Machines can also make work easier by changing the direction of the applied force.
Find the force needed to lift a 2000 N weight using a machine with a MA of 15.
133.33N
Calculate the MA of a hammer if the Force in is 125 N and the Forceout is 2000 N.
16
Find the efficiency of a machine that does 800 J of work if the Win is 2400 J.
33.33%
Find the force a person exerts in pulling a wagon 20 m if 1500 J of work is done.
75J
How does a ramp make lifting an object easier?
Less force is needed to lift an object when using a ramp
What is the formula for input and output?
M.A.= output/Input
Calculate the mechanical advantage of a hammer if the input force is 125 N and the output force is 2,000 N.
MA=F (out)/F (in) MA= 16
How do you make work easier?
Machines can make work easier by increasing the force that can be applied to an object.
Name two things in your life that require work (physics). Name two things in your life that require power (the rate at which work is done).
Me moving a chair. Moving a desk Chromebook & phone
What is mechanical advantage?
Mechanical advantage is the ratio of output force to the input force of the machine
Is work being done when... A roofers assistant carries a bundle of shingles across a construction site.
No
What two condtions needed for work?
One is that the applied force must make the object move The movement must be in the same direction as the applied force.
What is power?
Power is the amount of work being done in one SECOND It is a rate, the rate at which work is DONE
Describe a situation in which a force is applied but no work is done.
Pushing against an unmovable wall
Think Critically: The mechanical advantage of a machine is less than one. Why is this a bad machine?
This means there is less input force and even less output force. The machine barely has any MA which makes it like the same as doing it without the machine. You are doing more than the machine Output force is always greater than the input force
What is an Input and output?
Two forces that are involved when a machine is used to do work
Classify a screwdriver being used to turn a screw as one of the six types of simple machines.
Wheel and Axle
Label the parts of a bicycle that are simple machines.
Wheel: wheel and axle Petals/chains: pulley Handlebars: lever Gears Brakes levers Screws
How is work and energy related?
When work is done a transfer of energy occurs
Explain how work and energy are related.
Work is the transfer of Energy
Is work being done when... A worker lifts bricks, one at a time, from the ground to the back of a truck.
Yes
Is work being done when... a. A person shovels snow off a sidewalk.
Yes, because they are lifting the snow and moving the snow.
lever
a bar that moves around a set point
machine
a machine does not reduce work just makes it easier
simple machine
does work using one movement
Find the efficiency of a machine that does 800 J of work if the input work is 2,400 J.
eff= W (out)/W (in) x 100% 33%
A machine with more high efficiency produces?
less heat from friction
Work
the energy transferred when a force makes an object move over a distance.
first class lever
the fulcrum is in the middle of the lever
