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Balloon Rockets ANSWERS
Pre-Lab Questions
The diagram below shows a stationary cart on a frictionless surface. Two unequal opposing forces are about to be applied
to the cart.
1.
If the unequal opposing forces are applied to the cart at the same time, what will occur?
A.
B.
C.
D.
2.
The cart will move to the left with 90 N of force.
The cart will move to the right with 90 N of force.
The cart will alternate between moving left with 270 N and right with 360 N of force.
The cart will remain stationary.
Which two factors determine the gravitational attraction between two objects?
A.
B.
3.
time and temperature
shape and orbital speed
color and hardness
mass and distance apart
As altitude increases, air pressure
A.
B.
C.
4.
C.
D.
decreases
increases
remains the same
Student A and Student B sit on opposite ends of a see – saw. Student A weighs 45 kg while Student B weighs 60 kg.
When they lift their feet, who will hit the ground?
A.
B.
C.
D.
A
B
neither student
both students
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5.
A marble is dropped in a glass of water. Which force pulls the marble to the bottom of the glass?
A.
B.
6.
electricity
C.
gravity
friction
D.
magnetism
What is the most accurate description of gravity?
A.
B.
C.
D.
Gravity is a non-contact force that we have on Earth
Gravity is the strongest non-contact force in the universe
Gravity is a non-contact force between all objects that have mass
Gravity is a non-contact force that is very weak
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Actual Lab
KEY QUESTION/STATEMENT OF PROBLEM
How does adding mass to a balloon rocket will affect the speed of the balloon?
BACKGROUND
Newton's 1st Law of Motion is also called the Law of Inertia. Inertia is the ability of a substance to resist
changes in motion. The amount of motion depends on the object's mass.
Newton's 2nd Law of Motion can be expressed as force equals mass times acceleration. It explains that
force causes acceleration and mass resists acceleration. The more mass, the more force you need to make the
object move. Acceleration is calculated by dividing change in velocity (final speed – initial speed) by time.
Newton's 3rd Law of Motion says that for every action force, there is a reaction force equal in strength and
opposite in direction. The action/reaction forces act on separate objects, not the same object. Rockets use
Newton's 3rd Law of Motion to help propel them. Traveling into space requires large amounts of energy! In
this activity, you will use Newton's 3rd Law of Motion to propel balloons (different masses) across the
classroom. The balloons will be powered by escaping air, providing thrust, using Newton's 3rd Law of
Motion. Their motion is determined by Newton's 1st and 2nd Laws of Motion.
Lab Objectives
You will also use ALL of Newton's Laws to explain the movement of the balloon from launch until it stops.
HYPOTHESIS
Look at the key question above. Create a hypothesis (include a because).
If the mass of a balloon is increased, then the acceleration will decrease (when using the same amount of force)
because Force = Mass x Acceleration. If force stays the same and mass increases, acceleration has to decrease.
It will also USE up a significant amount of force (thrust) to get the heavier balloons moving because they have
more inertia/momentum (due to mass).
MATERIALS
1 balloon
1 straw
string or fishing line
tape
clamp
meter stick
1stopwatch
6 pennies
calculator
SAFETY CONCERNS
Follow general safety procedures.
Limit the amount of walking around to reduce the risk of running into another group's set up. NO
HORSEPLAY!
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ProcedureAlready set up:
1. A tape measure set up for you along the floor to measure distance.
2. Fishing line across the classroom (path for the balloon) pulled VERY tight (SO BE CAREFUL!).
3. A straw threaded by the fishing line at one end.
Procedure for your groups:
1. Make sure the string is pulled tightly and clamped down (with straw already threaded).
2. Inflate your balloon with enough air to consider it full, but so you know it won’t pop. Look at Mrs.
Twedt’s example. Don't tie the balloon!
3. Measure the circumference of the balloon and record it on the table. You will need to know this for
EVERY trial because it is a CONSTANT in your experiment.
4. Tape the straw on top of the balloon (standing at one end of the string, so it can travel the distance of the string).
5. Determine who your timers are. (You should have more than one (a backup timer) in case of human
error. If they are close, average them for your data table).
6. Let go of the balloon. MAKE SURE you measure the travel time of the balloon.
7. Record the travel time (in seconds)
8. Measure the distance the balloon travelled and record (front of the balloon).
9. Repeat steps 2-8 for 2 more trials with THIS balloon.
10. Repeat steps 2-9, Adding 3 pennies for the next 3 trials. TRY VERY HARD TO NEVER REMOVE
THE STRAW SO THAT RETAPING it doesn’t HAVE to happen.
11. Repeat steps 2-11, Adding 3 MORE pennies for the next 3 trials. TRY VERY HARD TO NEVER
REMOVE THE STRAW SO THAT RETAPING it doesn’t HAVE to happen.
12. Calculate your Average (Best Value) for Distance (and record) for each balloon.
13. Calculate your Average (Best Value) for Time (and record) for each balloon.
14. Calculate the average (final) speed of the balloon using your Average (Best Value) data for distance and
time (and record). S = D/T.
15. Calculate overall acceleration for your balloon. (Final Speed-Initial Speed)/ Time.
16. ANALYZE your data!
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Data
Circumference of your balloon initially = ____________ cm. **All other trials must match this.
Data Table: How mass affects acceleration of balloons
Distance
(Meters)
Balloon
Masses
Trial
1
Trial
2
Trial
3
Balloon
Balloon
+3
pennies
Balloon
+6
pennies
(Trial 1 + Trial 2 + Trial 3)
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Travel Time
(Seconds)
Average
(Best Value)
DISTANCE
Initial
Time
(Seconds)
Trial
1
Trial
2
Trial
3
Average
(Best
Value)
TIME
Initial
Speed
(M/S)
Speed at a
stop is
0 m/s
0 sec
0 m/s
0 sec
0 m/s
0 sec
0 m/s
(Trial 1 + Trial 2 + Trial 3)
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Final
Speed
(M/S)
Acceleration
(M/S2)
Fastest
Fastest
Slowest
Slowest
Average
Distance
Average
Time
Final Speed –
Initial Speed
Average
Time
Test Variable= Mass of the Balloon
Outcome Variable = Speed (acceleration) of the balloon)
Constants= Balloon, fishing line, placement of mass, pennies
Control Group = The trials without added mass (control group is the group
of the experiment that doesn’t contain the variable…it is used to compare
results to).
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Conclusion Questions
1. Which balloon accelerated the fastest? The balloon with no added mass
Which balloon accelerated the slowest? The balloon with 6 pennies (the most mass)
SO……explain: How did adding mass to the balloon affect the overall motion of the balloon?
F=MxA
The force was always the same because the balloons were all supposed to be the same size
(producing the same amount of thrust). SO mathematically speaking, increasing Mass means
decreasing Acceleration.
2. THINK- If the string did not have enough TENSION (force), what would eventually happen to the
motion of the balloon? Explain.
Without Tension, Gravity would not be balanced by the Normal force of the fishing line. The
balloon would want to fall, but due to the string, it wouldn’t…..It would spin up and down due
to thrust propelling it forward (yet it wants to fall).
3. Draw a diagram showing all the forces acting on the balloon to make them accelerate/while they were
accelerating (think about our centers….the book on the table in Center 2).
Gravity
Air Pressure and Elastic
Drag and friction
Thrust is expelled (Action)
Balloon moving through air
due to thrust (Reaction)
Normal Force and Tension
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Interpret the motion of the balloon using all 3 of Newton’s laws of motion (given below):
1st law: An object in motion stays in motion (at a constant velocity) and an object at rest stays at
rest, until acted upon by an unbalanced (outside) force.
1st law—object stays in motion unless acted on by an
unbalanced force = drag, friction, air pressure, if it hit the clamp
at the end, gravity
1st law explains that the balloon doesn’t move until the force (air)
is put inside it; it will not move forever because gravity and
friction and/or lack of air (thrust) will slow it down.
2nd law: The relationship between an object's mass m, its acceleration a, and the applied force F is F
= ma. Acceleration and force are vectors; in this law the direction of the force vector is
the same as the direction of the acceleration vector. *Remember, there are 3 parts to this
law. Which part of the second law is being addressed in this lab.
2nd law – F = MxA
The 2nd law explains to us that the balloon has a small mass (1
– 2 grams) that is accelerated by the force provided by the air
pressure inside the balloon
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F is always the same!!!! SO Mass Increases and Acceleration
Decreases!
*Think sports car and semi-----sports car—Who accelerates
faster? This is same as balloon with no mass and balloon with
mass….
3rd law: For every action there is an equal and opposite reaction.
3rd law – Action and Reaction. The action of
the thrust coming out of the balloon (due to
outside forces and pressure within the
balloon) (Action) propels the balloon in the
opposite direction of the thrust (reaction).
1. The word “air” should be accompanied by an arrow pointing left; the word “balloon” should be
accompanied by an arrow pointing right.
2. Both the distance traveled and time elapsed are needed to accurately measure/calculate the speed of a
moving object. Speed = distance/time.
3. The balloon may accelerate more slowly; the balloon may have more momentum; the balloon will not go
as fast or as far (multiple answers acceptable depending on student logic/explanation for answer given).
4. The balloon will eventually stop because the forces of gravity and friction will slow it down; the balloon
will run out of air and have no more force propelling it forward.
5. & 7. Teacher should create graph themselves for comparison with student graphs.
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