Activity 2b
Newton’s Third Law – Blow on a Sail
Name:_____________________________
PHYS 010
Date:______________________________
Partners:__________________________
__________________________
__________________________
Purpose:
To demonstrate Newton’s 3rd law.
Materials:
1. Low-friction cart
2. Small battery-powered fan assembly
3. 2 rubber bands
4. Masking tape
5. Piece of poster board / cereal box board for “sail”
6. Battery
7. 2 alligator clips
Diagram:
Rev 09-01
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Activity 2b
Newton’s Third Law – Blow on a Sail
PHYS 010
Procedure:
1.
Loop one of the rubber bands around the nut on the front of the
car, stretch the band over the top of the car, and then around
the base of the fan mount. To balance out the pull on the fan, do
the same with a second rubber band, but pass the band under
the car.
2.
Take care that the fan mount is high enough so the fan itself
doesn’t hit the top of the cart when it spins.
3.
Secure the bottom of the fan mount to the car with a couple
pieces of tape.
4.
Hook up the motor to a battery (make sure the leads don’t drag
on the floor).
Observe! What happens when you start the fan? In what direction is
the cart moving? Is this what you would have predicted?
5.
Affix the piece of poster board to the front of the car by poking
the screw through the paper. Tighten the nut to secure the sail.
Predict! What will happen when you connect the battery to the fan?
Observe! Go ahead and connect the battery to the fan. What happens
to the cart?
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Activity 2b
Newton’s Third Law – Blow on a Sail
PHYS 010
Questions:
1. Before you affixed the sail to your cart, why did the cart move in the opposite
direction of the wind?
2. Why didn’t the cart move after you added the sail?
3. This is an example of Newton’s Third Law which states that for every action,
there is an equal and opposite reaction. Provide the action-reaction pairs for the
following situations:
a) The lunar module takes off from the moon.
b) A car collides with a tree
c) A fish swims through the water
4. Newton’s Third Law Questions:
a) When a mosquito strikes your car windshield, is the force on the mosquito
greater than, or less than, or equal to, the force on the car? Why does the
mosquito suffer more damage?
b) When you fire a rifle, the bullet accelerates, and the gun recoils. Is the
acceleration of the gun equal to, greater than, or less than the acceleration
of the bullet?
Rev 09-01
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Activity 2b
Newton’s Third Law – Blow on a Sail
PHYS 010
Summary and Suggestions for the Future:
a. What were the main things that you learned from this activity?
b.
Can you think of alternative hands-on ways in which these concepts could be
demonstrated?
c.
What changes (if any) would you make to teach these activities in a Grade 7-8
classroom
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