Download Lab Write-Up

Lab Write-Up
Simple Machines and Their Forces
Objective:
1. To determine how forces add in a balanced system.
a. Vector addition using diagrams.
b. Free body diagrams
2. To examine the relationship between applied force and the resulting force due to
the setup. (Mechanical Advantage)
3. To use simple machine to calculate work, distance, force, gravitational potential
energy, and height.
4. To examine the principle of Conservation Of Energy as applied to simple
machines.
Review Formulas:
1. W=Fd (Work=Force x distance along the direction of the force)
2. W=mgh (Work=mass x gravitational potential energy x height)
3. Energy = KE + PE +Work (examine systems at rest KE=0)
4. E1 = E2 Conservation of Energy
Part One:
There are two methods to measure force. You can use either the spring meter or weight
on a string. The force mg is directed along the string. Keep in mind that the spring meter
is measured in grams. Using the pulley, apply both the spring meter and the weight on
the string to calculate the force. Draw a diagram of both methods in the space below.
Does the direction of the string change the Force? ___________ Have an instructor
initial your response.
Which method seems more accurate and stable?
The key point here is to allow the student to understand that weight is a force that is
convenient to use in these measurements but not critical. The first simple system is a
good place to check your free body diagrams and force balance.
Part Two:
Four different setup (3 are simple machines: the lever, the pulley, and the incline plane)
have been set up around the room,. Each group will have a chance to work with each
machine. For each machine:
1. balance the forces
2. determine what is the weight for the problem (may need to include pulley).
3. identify all forces acting on the weight
4. identify the applied force
5. draw a free body diagram
6. sum these forces by during the forces at the correct angle and length proportional
to force.
What is the total force on the weight?
How do the applied force and the weight compare ?
Lift the weight but keep the system in balance. This requires that you increase the applied
force by a very small amount for a very short time. If there are frictional forces in the
system you may need to apply a force to compensate for their impact. We will perform
our analysis by idealizing the system. We assume we can predict how the system would
behave if these forces were not present and we account for their effect on the
measurement.
Is the work on one side equal to the work on the other? ______________________
Pulley: Fill in the chart below:
# Of Pulleys
1
2
Force 1
Force 2
Ratio
Summarize each section by stating the relationship between applied force and used force
(support the weight). Comment on Mechanical Advantage and conservation of force
Summarize each section by a discussion of the energy transfer and the Conservation of
Energy Principle.
Part Three: Potential Energy and Work.
1.
2.
3.
4.
5.
Lift a weight up.
Draw the diagram
Calculate the work done by gravity.
Calculate the work done by you.
Calculate the change in the potential energy of gravity.
Write a statement that relates these three forms of energy and energy transfer. You may
need to consult with the instructor to clarify this point.
Each student must turn in a report.
Free Body Diagram four systems (id applied and the used force)
Vector Sum of Balanced Forces four system
Force summary statement four systems
Work calculation with picture four systems
Energy summary statement
Relationship between work and potential energy
Lever Activity:
Mass
Mass 1
100g
100g
100g
Pulley Activity:
Balancing Forces
Distance Moved From Fulcrum
Change in Mass vs. Change in Distance
Distance 1
Mass 2
Distance 2
100g
200g
300g
# of Ropes
Mass 1
Mass 2
Distance 1
Distance 2
Simple Machine’s Lab
Station: The Inclined Plane
What is the Inclined Plane?
A slanting surface connecting a lower level to a higher level. Things move up or down it.
A couple everyday examples where you would find one would be a slide, stairs, ramp,
hill or roller coaster.
What forces act upon an inclined plane?
1) Normal Force: Any perpendicular force coming from the surface. This force
counteracts gravity; what the object feels on top of a surface, nothing can pass
through the surface.
2) String force: the force coming from the weight that is suspended from the string
3) Gravitational force: Attracts objects to the center of the earth. Gravity is 9.8 m/s,
but we will assume for this lab it is 10m/s.
Steps:
1) Put the car on the track and level the track.
How did you level the track? How did u know the track was level?
What force is acting upon the track when it is leveled?
Draw a free body diagram with a level track
Calculate the force applied by the car by using the formula F=mg. (Remember
that for this lab, we will assume that g=10m/s and that mass is calculated in Kg)
2) Now lower the track
What do you observe happens to the car when you lower the track?
Why does the car move when you lower the plane (track)?
3) For the next step, I would like you to get different attach weights on the string and
your goal here is to balance this simple machine. Do about 4-5 different trials
with the track at different angles.
What different masses do you need to balance the simple machine when the track
is at different angles?
Remember: m(car)=m(hanging from string) to achieve a simple machine “in balance”.
Write down your finding below:
Alternative inclined plane group lead step by step:
1 Find the mass of the cart.
mass
units
2 Lay the track flat. Observe the motion.
Describe the motion:
What are the forces?
Draw the free body diagram for the cart.
3 Angle the track. Observe the motion.
Describe the motion:
What are the forces?
Draw the free body diagram for the cart.
4 Balance the cart with a weight and string. Knowing the weight and the tension find the
normal force (graphical vector addition).
5 Using the normal force can you show why the cart moved in part 3 ? Illustrate with a
drawing.
A 500 gram cart is on an incline at an angle of 30 degrees. Find the mass that must be
suspended on a string to keep the cart in balance. Show your work. Be sure to draw and
label the forces. Use a ruler and a protractor to get the angles and magnitudes correct.
If we want to examine this system using conservation of energy describe the two
scenarios that one should compare. State how conservation of energy applies in this
comparison.
6 Predict what will happen if you change the angle and verify your prediction.