- University of Virginia
- Physics Department
A Physical Science Activity
Action and Reaction
2003 Virginia SOLs
- identify action-reaction force pairs;
- understand applications of Newton's Third Law of Motion.
Discrepant Event - Soda Bottle Rocket
- 2-liter plastic soda bottle, empty
- Cork to fit bottle
- 200 ml vinegar
- 3 tablespoons baking soda
- 3 sheets aluminum foil, each 3 cm x 10 cm
- Safety goggles
*Take care that the bottle opening does not face in the
direction of any people or breakable objects during this
demonstration. Wear goggles throughout*
- Pour 200 ml vinegar into the plastic soda bottle. Place a cork in the mouth
of the container.
- Make a v-shaped envelope out of the sheets of foil, folding one sheet over
the top of the other to make the envelope thicker. This envelope should be
small enough to fit through the mouth of the bottle.
- Fill the envelope with 3 tablespoons of baking soda.
- Remove the cork from the soda bottle, taking care not to spill the vinegar.
Insert the aluminum envelope through the mouth of the bottle, being careful
not to mix the vinegar and baking soda.
- Quickly reseal the bottle.
- Standing to the side, rapidly rotate the bottle so that the baking soda
mixes with the vinegar. Stand back and observe.
- The cork should shoot from the mouth of the bottle forward, in turn propelling
the bottle backwards. The action is the cork, the reaction is the bottle movement.
Optional Bottle Rocket Launcher
For full and detailed instructions on the construction of this device, click
This device also uses a 2-Liter bottle as a rocket, but uses a more complicated
mechanism to achieve much higher air pressure within the bottle for greater
- launch apparatus (see above)
- 2 liter bottle
- bicycle pump (foot pump with pressure gauge works well)
- pressure gauge (either built into apparatus or attached to bicycle pump)
- 4 anchor spikes and hammer
- Put a spike in each of the anchor holes and use the hammer to secure them
into the ground. Attach the bicycle pump to the tire valve stem.
- Check to make sure that the opening of your empty 2-liter soda bottle will
fit over the PVC pipe. It should be a close fit, but some bottles are irregular
and may not work.
- Add varying amounts of water to the bottle (0% to 100% full). Quickly turn
the bottle upside down so that the neck is over the air inlet hole.
- Pivot the 1' steel bars inward so that they go over the bottle lip and
under the 3" steel bar.
- Tighten the wing nut above the compression spring to secure the bottle
and make a tight seal.
- Using the bicycle pump, increase the pressure in the bottle to about 40
psi. Be sure that nobody is above the bottle, then pull the string to remove
the steel bars and thus launch the rocket.
- Observe the motion and record your results.
Note: The industrial specifications for the pop bottles maintain that the
bottles can withstand 180 psi. For maximum safety, do not exceed 90 psi.
Newton's Third Law of Motion states that for every action done by
a force, there is an equal and opposite reaction by another force.
Forces always occur in pairs; one force is called an action force and
the other is called the reaction force. In the demonstration detailed
above, the action force is caused by carbon dioxide from the reaction
between vinegar and baking soda. The reaction gas causes pressure to
build inside the soda bottle, eventually pushing the cork from its
mouth. A result of this action is the movement of the soda bottle in
the opposite direction. This movement is caused by the reaction force
that stems from the original action. There are many other examples of
force pairs in everyday life. When you walk, your feet push on the
ground with a force. In return, the ground pushes on you with an
equal force, propelling you forward. A plate resting on a table
exerts a downward force on that table due to gravity. In return, the
table exerts an upward normal force on the plate.
In this experiment, the students are asked to explore two different action-reaction
pairs. Part one involves the motion of a balloon along a piece of fishing line.
If an inflated balloon is caused to release its air slowly, the force of the
air leaving the balloon will result in a reaction force, which launches the
balloon forward. In part two, the students will combine Alka Seltzer tablets
and water in a sealed Kodak film canister. This combination will produce carbon
dioxide, which will force the lid from the canister. Similar to the soda bottle
demonstration, the forward motion of the lid will induce a backward, reaction
motion of the canister. However, part two involves a second canister, which
will move as a result of the initial action, allowing it to be more visible.
The students should try each of these experiments a few times to completely
conceptualize action-reaction force pairs. Before they begin the experiment,
discuss and brainstorm with them other examples of these force pairs that are
found in the home or classroom.
To print out the Student Copy only,
- Long, cylindrical balloon (average size)
- 3 empty Kodak 35 mm film canisters
- Hot Wheels car track or model railroad track, 70 cm
- Cut a long piece of fishing line (5 m). Tie one end to the leg
of a chair.
- Inflate the balloon. While one person holds the opening
closed, tape a straw to the balloon parallel to its length.
- String the other end of the fishing line through the straw,
and tie that end to the leg of another chair approximately 5 m
from the first.
- Hold the inflated balloon near one chair, with the opening
facing the chair, and release it.
- Repeat this three times, each time trying to make the balloon
travel farther along the fishing line.
- Place the railroad or Hot Wheels track
on the table. Make sure that both ends of the track are pointing
away from people.
- Place an empty film canister, with its
cap, on the track. It should fit cleanly between the two rails of
- Pour water in another canister to a
depth of about 0.5 cm.
- Place 1/3 tablet of Alka Seltzer into
the canister and shake it for a second or two.
- Quickly place the canister on the track
so that the caps of the two canisters are touching. Step back. The
"loaded" canister should explode, pushing on the empty
- If the canister does not fire within two
minutes, carefully lift it from the track and slowly release any
internal pressure. Load another film canister and repeat.
- Measure the distance traveled by the
bullet (empty canister) and the cannon (full canister). Put the
data in the data table (see below).
- Fill the empty canister with water and
place it on the track.
- Reload the canister acting as a cannon
as described in steps 3 and 4. Place it quickly on the track and
- Measure the distance traveled by the
bullet (canister + water) and the cannon.
- Pour the water out of the bullet
canister and place the weight or washer inside. Place the canister
on the track.
- Repeat step 9. Measure the distance
traveled by the bullet (canister + weight) and the cannon.
To print out the Data Sheet only,
Distance by bullet (m)
Distance by cannon (m)
Trial I (empty bullet)
Trial II (canister + water)
Trial III (canister + weight)
1. Explain what caused the balloon to move across the
room in Part I in terms of Newton's 3rd Law. Identify the
force pair in this situation.
2. What caused the "bullet" canister to move in Part II?
Identify the force pair.
3. Explain the difference in the distance traveled by the "bullet" in
each of the three trials. Compare this with the distance traveled by the
4. Cannons that fire bullets are always very massive in
comparison with the bullet. Explain why this is necessary.
5. Identify the action-reaction pairs in the following
- a. A man steps from his boat to the dock.
- b. A textbook rests on a school desk.
- c. A tennis racket contacts a tennis ball.
Students with Special Needs
All students should be able to participate in this activity.
Click here for further
information on laboratories with students with special needs.
Data sheet to be completed during the laboratory.