Download Simple Machines

Simple Machines 2.notebook
January 12, 2016
Work and Energy
Work, Power, and Machines
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Simple Machines 2.notebook
January 12, 2016
Imagine trying to lift a car without a jack
You might be exerting a lot of force, but not moving the
It would feel like you have done a lot of work...but you
have actually done NONE
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Simple Machines 2.notebook
January 12, 2016
In science,
is done only when a force causes a
change in the position or motion of an object
work = force x distance
So what are the units we measure work in?
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Simple Machines 2.notebook
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Work is measured in a unit called
1 J = 1 Nm = 1 kgm
Imagine a father playing with his daughter by lifting her
repeatedly in the air. How much work does he do with each
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Simple Machines 2.notebook
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Imagine walking up a flight of stairs vs. running up a
Which is more exhausting?
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Simple Machines 2.notebook
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The amount of time it takes to do work is an
important factor
measures work in relation to time
power = work/time
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Simple Machines 2.notebook
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So what are our units for power?
Joules/second = Watt
watt (W) is the amount of power required to do 1 J of
This is about how much power you would need to lift an
apple over your head in 1 second
746 watts = 1 horsepower
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Simple Machines 2.notebook
January 12, 2016
It takes 100kJ of work to lift an elevator 18 m. If
this is done in 20 seconds, what is the average power
of the elevator during this process?
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Simple Machines 2.notebook
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Which is easier...lifting a car with a jack, or by yourself?
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Simple Machines 2.notebook
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Compare the amount of work required to lift a fourwheeler straight up onto the bed of a pickup, with
the amount of work required to push the same four-
The ramp allows you to apply a
larger distance, but the work done is the same
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Simple Machines 2.notebook
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allow us to do the same amount of work by
the distance while
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Simple Machines 2.notebook
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mechanical advantage
a machine describes how
mechanical advantage =
input distance
input force
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Simple Machines 2.notebook
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A machine with a mechanical advantage greater than 1
multiplies the input force
force, but increases distance and speed
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Simple Machines 2.notebook
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Calculate the mechanical advantage of a ramp that is
5.0 meters long and 1.5 meters high
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Simple Machines 2.notebook
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Simple Machines
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Simple Machines 2.notebook
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Simple Machines are the most basic machines
Other machines are modifications or combinations
There are two "families" of simple machines:
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Simple Machines 2.notebook
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The Lever Family
Levers are divided into three classes:
1st, 2nd, and 3rd Class
All levers have a rigid
point called the fulcrum
that pivots around a
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Simple Machines 2.notebook
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have a fulcrum located between
the input and output forces
Examples: Seesaw, hammer
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Simple Machines 2.notebook
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the arm and the input force is applied at the other
Examples: Wheelbarrow, two wheel cart (dolly)
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Simple Machines 2.notebook
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Third-Class Levers have a fulcrum at one end with
the output force on the other end.
The multiply distance rather than force.
Therefore have a mechanical advantage of less than 1
Examples: Forearm, Shovel
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Simple Machines 2.notebook
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Pulleys are modified levers because the pulley
itself is like the fulcrum of a lever
A single fixed pully has a mechanical advantage
of 1. All it does it change the direction of the
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Simple Machines 2.notebook
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A single movable pulley has a mechanical advantage of 2
Therefore you can lift a 100 pounds with only exerting
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Simple Machines 2.notebook
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Multiple pulleys can be used to get even higher
mechanical advantages
When multiple pulleys are put together in a single
unit it is called a
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Simple Machines 2.notebook
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wheel and axle is a lever or pulley connected to a shaft
A small input force can be applied and the force is
multiplied to become a large output force on the shaft
Steering wheel, screwdrivers, cranks
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Simple Machines 2.notebook
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The Inclined Plane Family
In inclined plane is basically a ramp
The input force is parallel to the ramp
object off the ground
Output Force
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Simple Machines 2.notebook
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Remember, incline planes work by spreading
the work out over a larger distance, which
decreases the force required!
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is a modified inclined plane
A wedge is two incline planes placed back to back
The wedge turns a single downward force into two
forces directed out to the sides
Examples: Axe, nail
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Simple Machines 2.notebook
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is an inclined plane wrapped around a cylinder
The steeper the threads, the ore force required to
Examples: Screws, jar lids, spiral staircase
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Simple Machines 2.notebook
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combines two or more simple
machines
A scissor: Uses two first class levers joined at a
single fulcrum AND a wedge that cuts into the paper
Bicycle: Wheel and axle, levers
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Simple Machines 2.notebook
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What is Energy?
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Simple Machines 2.notebook
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Remember, work is only done when an object
experiences a change in its position or motion
However, energy can be present in an object when
is the ability to do work
Energy and work are both expressed in units of
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Simple Machines 2.notebook
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A stretched rubber band (say on a slingshot) has
stored energy
Potential Energy
Often called "energy of position"
Think of an apple hanging form a tree...the energy
that could potentially do work on the apple results
from its position above the ground
This is called gravitational potential energy
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Simple Machines 2.notebook
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The equation to calculate gravitational potential energy is:
Potential energy = mass x free fall acceleration x height
PE = mgh
This means that potential energy is dependent on mass and
height
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Simple Machines 2.notebook
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A 65 kg rock climber ascends a cliff. What is the
climber's gravitational potential energy at a point 35 m
above the base of the cliff?
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is the energy an object has because
of its motion
starts to fall it gains kinetic energy
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Simple Machines 2.notebook
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The equation for calculating kinetic energy is:
Kinetic energy = 1/2 x mass x speed squared
kinetic energy?
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Simple Machines 2.notebook
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What is the kinetic energy of a 44 kg cheetah running
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The sum of potential energy and kinetic energy is
mechanical energy
Are there any other forms of energy?
We eat it for energy right?
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Simple Machines 2.notebook
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Energy that does not affect the motion of an object is
nonmechanical energy
Atoms and molecules have kinetic energy because they are
moving on an atomic scale
Chemical reactions involve potential energy
- Chemical bonds store energy
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