EXPLORE: Identify all simple machines used in the vehicle.
You have assembled mousetrap vehicle (MTV) kit. Examine the parts, pieces, and functions of
the MTV and make a list of simple machines within the MTV. You have five (5) minutes to
identify the simple machines and to justify why you believe those are simple machines.
A.
A mousetrap powered car is a vehicle that uses a mouse trap for a motor. There are many
different ideas, but the most common (and probably most successful) idea is to attach one
end of a string to the arm on the mousetrap, and the other end of the string is wound around
an axle. Pull back the mousetrap lever arm, wind the string on the axle, and let it go!
Please explain the kinematics changes that take place in the mousetrap vehicle (MTV) after
the trap’s bail arm is released. You can include relationships to demonstrate your
understanding of concepts, but NOT formulas. Your answer should discuss specifics of the
dynamic changes in an MTV:
- Velocity, Acceleration (Linear and Rotational)
- Inertia, Force (Friction, Weight, Applied)
- Torque, Moment of Inertia, Centripetal Force
- Conservation of Momentum (Linear and Rotational)
- Conservation of Energy (Kinetic and Potential)
- Simple Machines; Work; Power
Science Sunshine State Standards
SC.912.N.4.1
Explain how scientific knowledge and reasoning provide an empirically-based
perspective to inform society's decision making.
SC.912.P.10.1
Differentiate among the various forms of energy and recognize that they can be
transformed from one form to others.
SC.912.P.10.2
Explore the Law of Conservation of Energy by differentiating among open, closed, and
isolated systems and explain that the total energy in an isolated system is a conserved
quantity.
SC.912.P.10.3
Compare and contrast work and power qualitatively and quantitatively.
SC.912.P.12.1
Distinguish between scalar and vector quantities and assess which should be used to
describe an event.
SC.912.P.12.2
Analyze the motion of an object in terms of its position, velocity, and acceleration (with
respect to a frame of reference) as functions of time.
SC.912.P.12.3
Interpret and apply Newton's three laws of motion.
SC.912.P.12.4
Describe how the gravitational force between two objects depends on their masses and
the distance between them.
SC.912.P.12.5
Apply the law of conservation of linear momentum to interactions, such as collisions
between objects.
SC.912.P.12.6
Qualitatively apply the concept of angular momentum
Old Benchmark:
SC.B.1.4.7 The student knows that the total amount of usable energy always
decreases, even though the total amount of energy is conserved in any transfer.
SC.C.1.4.2 The student knows that any change in velocity is an acceleration.
SC.C.2.4.6 The student explains that all forces come in pairs commonly called action
and reaction.
Scoring Guide/Rubric
4 points
A score of four indicates that the student has demonstrated a thorough understanding of
the scientific concepts and/or procedures embodied in the task. The student has
completed the task correctly, used scientifically sound procedures, and provided clear
and complete explanations and interpretations.
The response may contain minor flaws that do not detract from a demonstration of a
thorough understanding.
3 points
A score of three indicates that the student has demonstrated an understanding of the
scientific concepts and/or procedures embodied in the task. The student’s response to
the task is essentially correct, but the scientific procedures, explanations, and/or
interpretations provided are not thorough.
The response may contain minor flaws that reflect inattentiveness or indicate some
misunderstanding of the underlying scientific concepts and/or procedures.
2 points
A score of two indicates that the student has demonstrated only a partial understanding
of the scientific concepts and/or procedures embodied in the task. Although the student
may have arrived at an acceptable conclusion or provided an adequate interpretation of
the task, the student’s work lacks an essential understanding of the underlying scientific
concepts and/or procedures.
The response may contain errors related to misunderstanding important aspects of the
task, misuse of scientific procedures/processes, or faulty interpretations of results.
1 point
A score of one indicates that the student has demonstrated a very limited understanding
of the scientific concepts and/or procedures embodied in the task. The student’s
response is incomplete and exhibits many flaws. Although the student’s response has
addressed some of the conditions of the task, the student has reached an inadequate
conclusion and/or provided reasoning that is faulty or incomplete.
The response exhibits many flaws or may be incomplete.
0 points
A score of zero indicates that the student has provided a completely incorrect solution or
uninterpretable response, or no response at all.
Potential Energy is stored when the trap’s spring is loaded, and when the string is
wound around a drive axle.
Kinetic Energy is created when the mouse-trap’s arm is released. The tension of the
mouse-trap’s arm pulls the string off the drive axle causing the drive axle and the
wheels to rotate, propelling the vehicle.
Work done will equal the Force applied from the mouse-trap arm times the distance the
MTV travels.
The initial velocity of the MTV will be 0 m/s as it is at rest.
The MTV acceleration as it goes from rest to its maximum velocity. This acceleration
will equal the product of its mass divided by the force from the torque.
Torque is generated by the mouse-trap’s lever arm swinging through its radius length.
The level arm pulls the string wound around the axle, causing the axle to experience a
centripetal acceleration.
The weight of the MTV is equal to the mass times gravitational acceleration (980 cm/s2)
The frictional force the MTV encounters is equal to the normal force (the reaction force
of the surface to the weight) times the coefficient of the competition floor.
The momentum of the MTV is equal to its mass times its average velocity. Its kinetic
energy is equal to its mass times its average velocity squared. Its kinetic energy will
equal its potential energy that was stored when the spring was loaded and the string
wound around the axle.
Sample Student Responses
4
4
4
3
There are many variables that affect the motion of the mousetrap powered
car. The biggest variable is the torque of the level arm snapping forward. This
level is connected to a string which spins the back axle in order for the car to
go forward. The more torque, the faster the back axle will spin, the fast the
wheel rotate. This turning of the wheels will accelerate the car forward. Now
inertia will affect the car. The thinner the tires, the less friction there will
be. The weight affects how far the car goes. If a heavier car is made to go a
certain speed, it will take longer to slow down, while a lighter car may be
accelerated more but will be easier to slow down. This is momentum which is
related to its kinetic energy (mv vs. ½ mv^2)
Work is accomplished by the arm of the trap pulling the string and turning
potential energy of the axel in a spinning axle with kinetic energy. The
rotational acceleration of the axle will increase the linear velocity as
momentum of the car makes it easier for the level arm to pull the string from
around the axle. The force of weight and the force of friction will be working
against the applied force in pulling the car down. The force of the lever arm
will increase if its length is increased, therefore increasing the torque.
Initially, the acceleration of the mousetrap vehicle is due to the torque
produced by the force of the spring pulling on the string. This causes
centripetal acceleration which, in turn, rotates the wheels. The amount of
velocity produced is affected by the length of the level arm which the string is
attached to. The longer the arm the more centripetal acceleration their will
be. Also, the larger the wheels the more distance it will travel before it comes
to a complete stop. When the level arm no longer generates and torque, it’s
momentum, calculated by the product of the mass and velocity, will be
interacted by friction and gravity causing the mousetrap to come to a complete
rest.
As the work increases, the velocity car acceleration increases. Inertia is based
on friction; the more friction, the lesser the acceleration. The wheight normal
and applied is also present. The heavier the vehicle, the stronger the
momentum but the lighter the vehicle, the lesser the momentum and the
centripetal force is in the tire when the lever arm swings, the string connected
will spin the axle causing the vehicle to go forward. The vehicle would go
farther and faster on a smoother surface but slower on a gagged or ruff
surface.
A torsion spring of a mousetrap is twisted through an angle of 1800. The torque vs angle data is given
below.
θ
N-m
rad
0.110
0.10
0.189
0.50
0.230
1.1
0.250
1.5
The amount of strain energy stored in the mousetrap spring in Joules is
0.2987
0.4174
0.8420
1562
----A student’s mousetrap vehicle has a mass of 25 grams. It crosses the 28 meter distance of the
gym floor in 60 seconds. How much force, in newtons, does the vehicle apply during its total
movement?