Lesson 2

Materials from the kit: parts to build a spring meter.
Not provided: an apple or small objects, soft plastic cup, hole punch, tape and scissors.

Students explore and measure forces: a force is a PUSH or a PULL.
They build their own simple spring meters to measure the PULL of gravity.
They eat an apple down until it weighs ONE newton.

1 What did you do last time? 2 Newton object inertia motion rest law PRINT the word next
to the image on the next slide.
PH-lesson 4 L3 res mot ine law obj new
4 Pull a wagon. What is a FORCE? A force is a push or a pull. PULL a chair
from a table.
Can you think of other things your can pull? Pull open a drawer. Pull a dog on a leash.
5 Push a shopping cart or a wagon. A Push is a FORCE A force is a PUSH or a PULL. Push a toy car or truck. Can you think of other things you can push? 6 You measure the PULL of gravity
on your body with a bath scale.

We measure this PULL in pounds
or newtons.
You know a lot about FORCES!
The Earth pulls down
on everything on its surface.
A force is a PUSH or a PULL.
7 You will need: You can build a device
that measures a PULL!
paper clip spring tape plastic tube paper scale screw
& nut
yellow tube
8 Measure a Force Build a spring scale to measure the force of a PULL. Unfold the paper
clip into an S shape.
Put the spring inside the yellow tube. 1 2 The hole in the yellow tube should be here. Line up the loop on the end
of the spring with the hole
in the yellow tube.
3 4 Hook the large end
of the paper clip through the holes
in the tube and
the loop in the spring.
9 Push the screw through
the holes in the outside tube
and the loop of the spring. Screw on the nut.
This holds the top of the spring
inside the tube.
Insert the yellow tube
inside the plastic tube.
5 6
10 7 8 Wrap the paper scale around the tube.
Tape the scale to itself.
Cut out the paper scale. Be sure that the scale
slides freely up and down
without sliding off the tube.
11 Congratulations! You just built a spring scale. hole punch To use your spring scale to measure a FORCE,
find these items:
soft plastic cup small apple
or other edible
12 Now you are ready to measure a FORCE! Punch a hole in the cup. Hold up the spring scale with the empty cup attached. Slide the paper scale
until the zero mark
lines up with the top of the yellow tube.
Hook the cup
to the paper clip
on your spring scale.
You just ZEROED the spring scale. 1 2 3
13 Nibbling to a Newton 4 5 Put the small apple into the cup
Hold up the spring scale.
The gravity of the Earth is pulling down on the apple.
You are measuring the force of that PULL with your spring scale.
What number on the scale does the
top of the yellow tube line up with?
This is the weight of your apple in NEWTONS.
Does it weigh more than ONE NEWTON? Most apples do.
How could you make your apple weigh only ONE NEWTON?
14 Now use your spring scale to measure the PULL of gravity on what is left of your apple. Take a bite out of your apple, of course! 6 7 8 Now measure how many marbles, dominoes or pennies, it takes
to PULL down on the spring with the FORCE of ONE Newton.
Be careful not to overstretch the spring on your scale. Keep nibbling on your apple until it weighs ONE NEWTON!
15 What is a newton of force? 16 You just used a SPRING to measure the pull of gravity
on an apple and other small objects.
The heavier the apple,
the FARTHER the spring
inside the meter STRETCHES!
Your goal in the next activity,
is to use the length of a spring
to determine the unknown weights.
Click for answer. How did the spring work
17 Determine the Unknown Weights FIRST click on Electra below. AFTER she finishes,
click on the red button.
What are the masses for the red, blue and green weights? One is equal, one is double
and one is halfway between.
Answers: 75 grams,
100 grams and 200 grams
18 Unbalanced Forces A Tug of War Add players when the cart is moving! FIRST click on Electra below. AFTER she finishes,
click on the red button.
19 When the cart is not moving,
AND the sum of the forces is ZERO, does the cart begin to move? WHY
When you add a player
to one side of a moving cart,
so that you balance the forces,

does the cart STOP? WHY
NO! The cart does not budge.
The pushes equal the pulls.
The forces are balanced.

There are no unbalanced forces
to overcome this INERTIA!
NO! The cart keeps on going!
The pushes equal the pulls.
The forces are balanced.

There is no unbalanced force
to overcome this INERTIA!
Add in a player
AFTER the cart
is moving!
20 It is only
when the forces are
that you can overcome UNBALANCED, INERTIA!
21 An object in motion tends to WHAT An object at rest
tends to WHAT
A force is a Newton's First Law
is also called the
1 2 3 4 5 An object at rest stays at
rest unless acted upon by
Law of Inertia stay in MOTION stay at REST PUSH or a PULL an unbalanced force
22 Force and
the First Law of Motion
Seat Belts, Head Rests and the Law of Inertia! Inertia and Outside Forces