Download What is Work?

What is Work?
Tuesday and Friday
Let’s review some of the big ideas we’ve
covered so far:
There are many forms of energy
Mechanical (kinetic energy and potential energy)
Electrical
Radiant (solar)
Thermal (heat)
Sound
Light
According to the law of conservation of energy,
energy cannot be created or destroyed, but it can be
transferred from one place to another and
transformed from one type to another.
Examples we have studied of how
energy can be transferred or
transformed:
• We have seen how thermal energy
can be transferred through
convection, conduction, and
radiation.
• We have seen how kinetic energy can
be converted into potential energy
and how potential energy can be
converted into kinetic energy.
• We investigated how the chemical
energy stored in a battery could be
transformed into electric energy and
then into sound or light or thermal
energy.
We’ve also seen how energy is
transformed in motors and generators:
A motor converts
electrical energy into
mechanical energy
A generator converts
mechanical energy into
electrical energy
We are now going to look at another
way that energy transfer can occur.
Energy can be transferred when two
objects interact and exert force on each
other.
When a force is used to move an object
done.
In order for work to be done:
• A force must be applied to an object and the
object must move a distance.
This woman is pushing on the cart
(exerting a force) and the cart is moving
a distance, so this woman is doing work
on the cart.
If the woman pushed the cart and the
cart did not move, then the woman
would do no work on the cart.
is
This man is lifting a box (exerting a
force) and the box is moving up a
distance, so this man is doing work on
the box.
If the man tried to lift the box and the
box did not move, then the man would
do no work on the box.
When work is done to an object and the object moves,
the work is transformed into kinetic energy!
When an object is lifted to a height, work is done
against gravity in lifting the object and is transformed into
potential energy!
Energy Basics (clip from Exploring Energy) – Discovery Education Streaming
Video: https://app.discoveryeducation.com/learn/videos/00450c51-b8f9-4be48b91-bf332041e70f?hasLocalHost=false
Note: For the link to work, you will need to be signed in to Discovery Education
using internet explorer.
You need to know…
Spring scales measure force
Force is measured in SI
units called newtons (N)
We will be measuring weight,
which is one kind of force.
Activity 1.3 – Explore 1
Measuring Force
Focus Question: How much force does it take
to lift an object?
Activity 1.3 – Explore 1
Measuring Force
1. Collect your materials.
2. Follow the procedure outlined on page 7 of your
team handbook.
3. Don’t forget to record your observations in your
science journal!
Object
1.
2.
3. Car with 10 washers
Weight (N)
Activity 1.3 – Explore 1
Measuring Force
1. How much did your car and washers
weigh?
2. How much force did it take to lift the car
and washers?
3. What is the unit that weight is measured
in?
4. Why do you think weight and force are
measured in the same units?
When you lifted the car, you did work on the car! (you
exerted a force and it made the car move up).
Anytime we lift an object we do work on it. The higher
you lift it, the more work you do on it.
Remember, work involves both force and distance!
In the next few activities we will be studying
. We will see how simple machines decrease
the effort force required to do work.
A simple machine is a device that reduces the
amount of effort force needed to do work by
increasing the distance that the force is applied.
Simple machines can also change the direction of the
effort force.
What is a Simple Machine?
What is a Machine?(clip from Real World Science: Simple Machines) – Discovery
Education Streaming Video:
https://app.discoveryeducation.com/learn/videos/3794a1b7-a59e-441a-9e87bd56976fffe8?hasLocalHost=false
Note: For the link to work, you will need to be signed in to Discovery Education
using internet explorer.
What
these
They
are alldo
examples
of
inclined
planes, the
first type
machines
have
inof
simple
machine we will study!
common?
An inclined plane is a
sloping surface, like a
ramp, that reduces the
amount of force required
to lift an object. It
is the first type of
simple machine that
we will be studying.
Activity 1.3 – Explore 2
Inclined Plane
Focus Question: How does an inclined plane
reduce the force needed to lift an object?
In this investigation, we will compare the
amount of force needed to lift the car to
the amount of force needed to pull the car
up an inclined plane.
Activity 1.3 – Explore 2
Inclined Plane
1. Collect your materials.
2. Follow the procedure outlined on page 9 of your
team handbook.
3. Record your data on
Student Sheet 1.3D!
Activity 1.3 – Explore 2
Inclined Plane
1. Graph your data using student sheet 1.3B.
Activity 1.3 – Explore 2
Inclined Plane
1. How much force did it take to lift the car?
2. How much force did it take to pull the car
up the shortest (steepest) ramp?
3. How much force did it take to pull the car
up the middle ramp?
4. How much force did it take to pull the car
up the longest (least steep) ramp?
5. Do you see a pattern? Look at your graph?
Do you see the same pattern?
No matter whether you lift the car straight up to the
top of the ramp, or pull the car up the ramp, it takes
the same amount of work!!
BUT, using the inclined plane requires less force to
pull the car, so the work is easier! However, you have
to move the car over a greater distance.
Machines increase the distance over which the force
is applied, which decreases the amount of force that
is required.
Machines let you do the same amount of work with
less force!!!
The box is going
to the same
height whether
you lift it or
push it up the
ramp, so it takes
the same
amount of
work.
But, pushing it
up the ramp is
easier than
lifting it straight
up.
The trade off is
that you have to
apply the force
over a longer
distance.
Inclined Planes
Inclined Plane (clip from Discovering Simple Machines: Inclined Plane, Wedge,
Screw)– Discovery Education Streaming Video:
https://app.discoveryeducation.com/learn/videos/a51b1ab2-5f82-4483-ad181c7ce2c0f0b9?hasLocalHost=false
Note: For the link to work, you will need to be signed in to Discovery Education
using internet explorer.
Click on picture for an interactive
activity on inclined planes
http://aspire.cosmic-ray.org/Labs/Machines/act2a/lab1.html
The wedge and the screw are 2 types
of simple machines that are related to
inclined planes.
A wedge is made of 2 inclined planes back-to-back.
Examples of wedges are nails, knife and axe blades.
A screw is an inclined plane wound around a
post or cylinder.
Screw and Wedge
Screw (clip from Real World Science: Simple Machines)– Discovery Education
Streaming Video: https://app.discoveryeducation.com/learn/videos/9047adf0767d-4040-b195-10cc84569f58
Note: For the link to work, you will need to be signed in to Discovery Education
using internet explorer.