Transcript What is work?

Definitions:
Energy: Ability to do work
Work= Force x Distance
Force: A Push or a Pull
What is work?
 In
science, the word work has a
different meaning than you may be
familiar with.
 The scientific definition of work is:
using a force to move an object a
distance (when both the force and
the motion of the object are in the
same direction.)
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Work or Not?

According to the
scientific
definition, what is
work and what is
not?


a student carrying a
book bag
a mouse pushing a
piece of cheese
with its nose across
the floor
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What’s work?
A
scientist delivers a speech to an
audience of his peers. No
 A body builder lifts 350 pounds above
his head. Yes
 A father carries her baby from room to
room. No

A mother pushes a baby in a carriage. Yes
A
teenager carries a 20 km grocery
bag to the car? No
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What are simple machines?
 Simple
machines are elementary
devices (including levers and pulleys)
that provide mechanical advantage.
Formula for work
Work = Force x Distance
 The
unit of force is newtons
 The unit of distance is meters
 The unit of work is newton-meters
 One newton-meter is equal to one joule
 So, the unit of work is a joule
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Work Equation


Work (joules) = force (newtons) X distance ( meters)
W=Fd
A painter lifts a can of
paint that weighs 40 N a
distance of 2 m. How
much work does she do?
TFSA Method
 T=
Title
 What
operation are you completing? What
are you looking for?
F
= Formula
 What
is the formula used to complete the
operation?
S
= Substitution
 This
is where you actually plug in the
numbers
A
= Answer
A painter lifts a can of paint that weighs
40 N a distance of 2 m. How much work
does she do?
 T=
Title
How much work does she do?
 F = Formula
Work = force X distance
 S = Substitution
force: f = 40 newtons
distance: d = 2 m
Work = (40n)(2m)
A
= Anwser
80 (N)(M)
80 Joules
Work = 80 Joules
Work Equation


Work (joules) = force (newtons) X distance ( meters)
W=Fd
A painter lifts a can of
paint that weighs 40 N a
distance of 2 m. How
much work does she do?
If you push a lawn mower, the horizontal
force is 300 N. If you push the mower a
distance of 500 m, how much work do you
do?
 Title: How much work do you do?
 Formula: Work = Force X Distance
 Substitute: W =(300n)(500m)
 Answer: W = 150,000 newtons meters
W = 150,000 Joules
Take a Closer Look at the
Six Simple Machines
Simple Machines all have one
thing in common:
 They
give their users some form of
advantage. They do 3 useful things:
1.
2.
3.
multiply effort
multiply distance
change direction of force
Definition:
Mechanical Advantage is a ratio of the
load or resistance to the effort or
force.
Simple Machines Can:
 Lift
and push objects
 put pressure on objects
 hold or break objects
The weight lifted, or the resistance
overcome, is the LOAD.
Definitions:
Load is the weight or resistance that is moved
using a simple machine.
Resistance is an opposing force tending to
prevent motion.
Effort is the force applied to move a load using
a simple machine.
Force is a push or a pull.
Fulcrum is the point at
which a lever arm picots.
Water in a hole to
deep to reach with
a bucket
A boulder too massive
to push, role or lift
Six Simple Machines
 They
give their users some form of
advantage. They do 3 useful things:
1. multiply effort
2. multiply distance
3. change direction of force
LEVER Activity
A lever is a tool that people use to make work
easier. Levers are used to lift things or to
overcome resistance. Levers give us an
advantage by making work easier.
A lever arm is a stick or beam free to pivot at
a point.
The fulcrum is the point around which the leve
arm pivots.
Rules for the Spring Scale
Newtons is the unit used to measure force in the
metric system.
1.) Always zero the scales before starting the day’s
activity.
2.) Always use the scale right side up, never upside
down.
3.) Pull until the lever arm is level, then read the
effort. This works best if one student pulls the scale
while the another reads the effort.
4.) Stop before the scale goes past the 10-N limit.
Inclined Planes

An inclined plane is
a flat surface that is
higher on one end
 Inclined planes
make the work of
moving things easier
Inclined Plane

The Egyptians used simple machines to build the
pyramids. One method was to build a very long
incline out of dirt that rose upward to the top of the
pyramid very gently. The blocks of stone were placed
on large logs (another type of simple machine - the
wheel and axle) and pushed slowly up the long,
gentle inclined plane to the top of the pyramid.
Screw
The screw is an inclined plane wound
around a central cylinder.
The mechanical advantage of an screw can be calculated
by dividing the circumference by the pitch of the screw.
Pitch equals 1/ number of turns per inch.
Wedges
Two inclined
planes joined
back to back.
 Wedges are used
to split things.

WHEEL AND AXEL

A ferris wheel is an
example of a wheel
and axle.
Wheel and axel are two
different-sized wheels that
turn together around the
same point.
Pulleys

Pulley are wheels
and axles with a
groove around the
outside
 A pulley needs a
rope, chain or belt
around the groove
to make it do work
First Class Lever
A Class-1 lever has the fulcrum located
somewhere between the effort and the load.
E = Effort
F = Fulcrum
L = Load
First Class Lever
.

Common examples
of first-class levers
include crowbars,
scissors, pliers, tin
snips and seesaws.
Second Class Lever
A Class-2 lever has the fulcrum located at one
end of a lever arm. The Load is between the
fulcrum and the effort has not changed.
F = Fulcrum
L = Load
E = Effort
Second Class Lever
 Examples
of
second-class
levers include
nut crackers,
wheel barrows,
doors, and
bottle openers.
Third Class Lever
A Class-3 lever the fulcrum is at one end, and
the effort is applied between the fulcrum and
the load. The direction of effort is not changed.
F = Fulcrum
E = Effort
L = Load
Third Class Lever
 Examples
of third-class
levers include tweezers,
broom, hammers, and
shovels.
Work and Power – Section 1 – Page 76
If you push a lawn mower, the horizontal
force is 300 N. If you push the mower a
distance of 500 m, how much work do you
do?
Work and Power – Section 1 – Page 76
If you push a lawn mower, the horizontal
force is 300 N. If you push the mower a
distance of 500 m, how much work do you
do?
 Title:
How much work do you do?
 Formula: Work = Force X Distance
 Substitute: W =(300n)(500m)
 Answer: W = 150,000 newtons meters
W = 150,000 Joules
Work and Power – Section 1 – Page 77
In the course of a short race, a car does
50,000 Joules of work in 7 seconds.
What is the power of the car during the
race?
Work and Power – Section 1 – Page 77
In the course of a short race, a car does
50,000 Joules of work in 7 seconds.
What is the power of the car during the
race?
 Title:
What is the power of the car
during the race?
 Formula: Power = Work / Seconds
 Substitute: P =50,000 J / 7 S
 Answer: P = 7,142.86 WATT
Work and Power –Sec 1
Pg 78
1.
Describe a situation in which work is
done on an object.
Evaluate which of the following
situation involves more power:
200 J of work done in 20 s or 50 j of work
done in 4 s? Explain
2.
200 J of work done in 20 s or
50 J of work done in 4 s?
 Title:
What is the power?
 Formula: Power = Work / Seconds
 Substitute: P =200 J / 20 S
 Answer: P = 10 WATTs
OR
 Title: What is the power?
 Formula: Power = Work / Seconds
 Substitute: P = 50 J / 4 S
 Answer: P = 12.5 WATTs
Work and Power –Sec 1
Pg 78
3. Determine two ways power can be
increased.
4. Calculate how much power, in watts, is
needed to cut a lawn in 50 minutes if
the work involved is 100,000 Joules.
Calculate how much power, in
watts, is needed to cut a lawn
in 50 minutes if the work
involved is 100,000 Joules.
 Title:
What is the power needed?
 Formula: Power = Work / Seconds
 Substitute: P =100,000 J / 3,000 S
 Answer: P = 33.33 WATTs
Work and Power –Sec 1
Pg 78
Think Critically:
Suppose you are pulling a wagon with the
handle at an angle. How can you make
your task easier?
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