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# Invisible Forces  Mystery 1

## How could you win a tug-of-war against a bunch of adults?

Beginning Exploration (1 of 11)
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Beginning Exploration (2 of 11)

DISCUSS:

Can you think of any way for your team to win? Is there something you could do to make it harder for the adults’ team to pull?

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Beginning Exploration (3 of 11)
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DISCUSS:

Is there some way to stop the adults from being able to push against the ground?

With any ideas you come up with, explain why you think that idea might work.

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Beginning Exploration (5 of 11)
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Beginning Exploration (6 of 11)

Practice: Think about each action below. For each one, ask yourself: Is it a push or a pull? (Answers on next slide.)

squeeze
pinch
tug
smack
drag
lift

Can you come up with any other verbs where there's either a pull or a push?

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Beginning Exploration (7 of 11)
squeeze pinch = push = push = pull = push = pull = It depends how you lift. You could push up on a thing to lift it, or you could pull on it too.
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Beginning Exploration (8 of 11)
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Beginning Exploration (9 of 11)

Discuss: Do you have any ideas for how you could get the watermelon to burst using rubber bands?

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Beginning Exploration (10 of 11)
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Beginning Exploration (11 of 11)

SPECIAL NOTE TO TEACHERS

The next slide features an Activity Video where students learn how to make "Hopper Poppers."

Constructing the hopper takes students about 20-25 minutes. Practicing using their hopper and then completing the "High Hop Score Card" takes an additional 20 minutes.

If your time is limited, there is a natural stopping point after Step 6. Have students write their names on materials, then collect them and resume the activity next science class.

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Beginning Activity Prep
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# Step 1: Print out materials and get supplies

To make and test a Hopper, each student needs:

• Enough “light chipboard” to cut a 3” x 6” rectangle — available at craft or office supply stores or on Amazon. (This chipboard is about as thick as the cardboard used to for cereal boxes, so you also have the option of raiding the recycling bin for supplies.)
• A ruler
• A pen
• Scissors
• 2 or 3 #16 rubber bands — available at craft or office supply stores or on Amazon. (These rubber bands are 1/16” wide and about 2” long, measured from one end of the loop to the other.)
• 1 High Hop Scorecard

It's never a bad idea for students to wear safety glasses, available for a good price here.

For open-ended exploration, the class will also need:

• Extra chipboard for students who want to make additional hoppers
• Rubber bands of different sizes and thicknesses

To help guide students during open-ended exploration, the teacher needs a printout of Teacher Tips .

# Step 2: Prepare for class

If you want your students to practice measuring, you can have them cut 3” x 6” rectangles from chipboard before you begin this mystery.

Otherwise, we recommend you cut the chipboard into 3” x 6” rectangles before class. It doesn’t take long if you use a paper cutter.

Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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Beginning Activity: Hopper Popper
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# Extra Activity: Tug-of-War

Tug-of-war is a great way to give students a feel for forces. You’ll need a sturdy rope, a room with a slick floor, and masking tape. Use masking tape to mark the center of the rope and make a line on the floor.

Discuss with the students how to make two, evenly matched tug-of-war teams. Have the teams play tug-of-war, starting with the center of the rope directly above the line.

Then have a rematch with one simple change: The winning team must take their shoes off and play in their stocking feet. (They’ll feel like teachers on roller skates.)

If students mention friction here, let them know you’ll be exploring that topic fully in a future Mystery.

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# Image & Video Credits

Mystery Science respects the intellectual property rights of the owners of visual assets. We make every effort to use images and videos under appropriate licenses from the owner or by reaching out to the owner to get explicit permission. If you are the owner of a visual and believe we are using it without permission, please contact us—we will reply promptly and make things right.

Exploration
watermelon by Mike Mozart , used under CC BY
Soldiers playing tug of war by SFC Victor Aguirre
push by Mark Doliner , used under CC BY
dough stretching by Joe Hall , used under CC BY