Sensors:
Loggers:
Science in
Sport
Force
Any EASYSENSE
Logging time: SnapShot with Asks
for Value function
401 Forces in levers
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In sport there are many cases where mechanical advantage created through levers and lever systems
is important. The aim of this investigation is to introduce the concept of levers and moments. An
understanding of the basic principles can then be applied to the need to learn a technique e.g. why it is
important to grip a javelin at a set place.
A machine is a device designed to make work easier. One of the simplest machines is the lever. This
simple device allows large forces to be applied to small areas e.g. to move heavy objects. A lever is a
long rigid bar that is rested on a support, which allows the bar to pivot. The support is called the
fulcrum.
Levers are divided into classes, first, second and third. In this experiment you will study a first class
lever. A first class lever is where the effort is one side of the fulcrum and the load is on the other.
The effort is the force you need to apply to make the load move. With the other classes of levers
force or distance are magnified. In third class lever systems (most common in sport and humans), the
force applied as a result of effort in is reduced, but the distance the object is moved is increased.
Remember that distance x time = speed, third class levers are used in human physiology to increase
speed not make the task easier. Good use of the levers in the body can increase the output speed.
A lever will work by increasing the force you exert. The increase in the applied force is called the
mechanical advantage and gives an indication of how many times the force has been increased.
In the experiment a rigid bar is positioned on a fulcrum, a mass is rested on the bar to one side of the
fulcrum, the force needed to balance the force generated by the mass is measured by a Force sensor.
From the results you will be able to calculate the mechanical advantage of the system. Using the Force
sensor allows you to measure the increase and decrease in force required to balance the beam.
Supporting the
Dynamics track to
make a balancing
beam.
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Attaching a Force sensor to the side of the
Dynamics track to measure forces needed to
balance the track.
What you need
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
An EASYSENSE logger.
A Smart Q Force sensor with hook fitted.
The track from the Dynamics system.
A 500 g mass.
Blu-Tack or sticky / masking tape.
2 small brackets from the Dynamics system.
2 M6 hex bolts and wing nuts from the Dynamics system.
A small block (matchbox).
Rubber band.
M6 Hex bolt.
What you need to do
1.
Check the Force Sensor has the hook attached. Connect the sensor to input 1 of the logger.
2. Position the fulcrum at the ½ way mark. Use a piece of masking tape to mark on the track the
fulcrum position, draw a line on the tape for the exact fulcrum line. Put an M6 hex bolt in the
slot on the side of the track with the distance scale.
3. Mark a position 40 cm away from the fulcrum on one side of the track. On the other side of
the fulcrum mark distances of 10, 20, 30 and 40 cm.
4. From the EasySense software’s Home screen select Open Setup (or File, Open Setup). Open
the file Data Harvest Investigations (Edition 2) \ Setup file \ Science in Sport V2 \ 401
Forces in levers.
5. Select Test Mode (Tools menu). Hold the Force sensor with the hook facing down and with no
additional mass on the sensor. Use the tare knob on the sensor to give a force reading of zero.
6. Hang the 500 g mass from the hook on the Force sensor, when the reading has stabilized
record the value.
7. Place the mass on the tack at a distance of 40 cm from the fulcrum (use a small piece of tape
or Blu-Tack to hold the mass in place).
8. Move the bolt so it is 10 cm from the fulcrum. Place the hook of the Force sensor over the bolt
and let it hang freely.
9. Click on Start, and pull down on the Force sensor to bring the track to balance. Click in the
graph area to record the value. A box will pop up asking for a value; enter 10 (the distance
from the fulcrum).
10. Repeat the process, leaving the mass at the 40 cm mark, but moving the Force sensor to the
20, 30 and finally the 40 cm mark from the fulcrum.
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Results and analysis
Add a Title to the graph and then Save the results. The results can be printed or copied into your
report document as required
1
Distance of
mass from
fulcrum dr
(m)
0.4
Force
produced by
the mass, Fr
(N)
Moment of
fixed mass
dr x Fr
(Nm)
2
0.4
0.3
3
0.4
0.2
4
0.4
0.1
Force sensor
distance, de
(m)
Measured
force from
sensor, Fe
(N)
Moment at
Force sensor
de x Fe
(Nm)
0.4
Calculations
Fr = resistance force, the force created by the attached mass.
Fe = effort force, the force measured by the Force sensor.
dr = the distance from the fulcrum to the mass
de = the distance from the fulcrum to the Force sensor.
TMA = theoretical mechanical advantage.
MA = mechanical advantage.
1.
Calculate the mechanical advantage for each of the 4 experiments. Use MA = Fr / Fe.
2. Calculate the theoretical mechanical advantage of the 4 experiments. Use TMA = dr / de.
3. Calculate the percentage difference between TMA and MA for each of the experiments.
Questions
1.
?
How does the force required to balance the fixed mass change as the Force sensor moves?
2. How does the moment change with the distance of the Force sensor from the fulcrum?
3. What happened to the mechanical advantage as you shortened the distance to the fulcrum for
the mass?
4. How did moving the mass closer to the fulcrum point affect the force needed to balance it?
5. What was the mechanical advantage of the first lever tested? Where would you use such a
lever?
6. What would account for the difference between the TMA and MA?
7. When you throw something like a javelin, what happens to the mechanical advantage if the arm
is bent?
8. Apart from maximising the advantage from levers, what forces / principles are being used in
the body movements before throwing a shot?
9. Think about a hurdle sprinter, how would knowledge of levers help in understanding the
technique used to cross the hurdle? Hint: think about the leg relative to the body as a lever
system.
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401 - 3