Experiment As with the primary experiment, we used a light gate to
collect another set of results.Manually timing the experiment: Added
weight (g) Time
taken to travel 2m (s) Velocity
[distance/time] (m/s) Average
speed (m/s) 0 3.51 3.44 3.32 0.64 0.58 0.61 0.61 200 2.33 2.17 2.13 0.86 0.92 0.94 0.91 400 2.26 2.15 2 0.88 0.93 1 0.94 600 2 2.15 2.16 1 0.93 0.93 0.95 800 2.1 2.21 2.21 0.95 0.95 0.9 0.94 1000 2.07 2.08 2.34 0.97 0.96 0.86 0.93 1200 2.2 2.31 2.29 0.91 0.87 0.87 0.89 Using a light gate and computer software: Added
weights (g) Speed
(m/s) Average
speed (m/s) 0 1.62 1.66 1.5 1.6 200 1.65 1.57 1.63 1.62 400 1.64 1.6 1.65 1.63 600 1.66 1.61 1.67 1.65 800 1.67 1.68 1.68 1.68 1000 1.68 1.69 1.7 1.69 1200 1.69 1.69 1.71 1.7 We repeated ALL results three times, even when using a light gate, to improve the accuracy
of our experiment.Skill Area A :
Analysing evidence and drawing conclusionsPrimary Experiment
The graph clearly shows the increase in speed as the height of the ramp
greatens, but not in a proportional manner. The slight curve suggests that
another force is acting on the trolley and not permitting it to increase speed
uniformly. Again, when using the light gate, the results clearly show
that there is a definite increase in speed as the height of the ramp expands. The
curve is slightly more prominent, and the peak speed reached in this part of
the experiment is almost double of that in the last.Conclusion My prediction was proved correct as the graphs clearly
show that the speed does indeed increase when the ramp is raised higher. This
is due to the fact that more potential energy is given to the trolley as it is
raised higher ? height is part of the formula that makes up P.E:P.E = mgh P.E = mass x gravity x heightSo the higher an object goes, the more gravitational
potential energy it gains. When it falls, it?s potential energy is converted
into kinetic energy and; since energy can neither be created or destroyed, only
converted; it will move at a faster speed.The vast difference in the manual timing speed and the
light gate speed is probably due to reaction time. The computer is able to
record the speed far more accurately than we can.So, to sum up, as you lift an object to a height, the
chemical energy stored in you (which comes from the food you eat) is converted
into gravitational potential energy. Obviously, the higher you lift the object,
the more energy you are using and therefore the more potential energy the
object is gaining. Potential energy is converted into kinetic energy completely
so the object when released will move at a faster rate depending on how high it
is lifted.Height does affect the speed at which a
trolley travels down a ramp
The graph shows no pattern. The speed stays roughly around the 0.9m/s mark
except for a suspected anomaly at the beginning. The graph again shows no significant increase in speed as
mass increases, but there is a slight increase nevertheless. It is again almost
double the speeds recorded in the manual timing experiment.Conclusion The first graph shows a wavering line, going up and then
down. This is expected from a manual timing experiment as results should vary
depending on our reaction time. There is an anomalous result with no weights
added ? this was due to the fact that the trolley hit the side when travelling
down the ramp, losing a lot of its energy on friction and a bit on sound which
drastically slowed it down, as depicted in the graph. Other than this, the
results tend to stay around the same speed. The second graph does show a little, but definite,
increase in speed. This is caused by the decrease in friction as more wheels
are added. The extra force pushing down on the wheels made them less prone to
losing their energy on the surface of the ramp ? but this effect is only very
slight. If we were to conduct this experiment in a place with no air resistance
and no friction, we would see that the speed of the trolley stayed perfectly
constant as mass plays no part in the equation of potential energy being
converted into kinetic.P.E = K.E Mgh = ½mv2 Mass x gravity x height = ½ x mass x
velocity2 Gravity x height = ½ x velocity2Mass is cancelled out and theoretically has no impact on
the speed of which an object travels when it is given gravitational potential
energy. Galileo proved this with his famous experiment-?…In the 17th Century, Galileo was the genius
who looked at this phenomenon with fresh eyes. Legend has it that he climbed to
the top of the leaning Tower of Pisa and dropped two cannon balls over the
side. One cannon ball was heavier than the other was. Galileo?s professor was
highly sceptical about Galileo?s idea and so Galileo had the professor lie at
the bottom of the tower with his ear to the ground! This was so that the
professor could listen out for the two thuds as one cannon ball hit the ground
before the other one. The professor was dismayed to only hear one thud ? they
had hit the ground at the same time!..? Taken
from Bev Aldridge?s PGCE NotesYou may say a feather drops slower than a cannon ball, but
it only flutters to the ground because of air resistance. Air resistance acts
on everything that moves through the air and is a force that opposes motion,
i.e. it makes a moving body slow down. Some shapes result in less air
resistance than others ? a feather experiences much, and a coin very little.
Thus when a coin and a feather are dropped from the same height in a vacuum,
they both hit the ground at the same time. This is an important principle in science. If air
resistance is the same for two objects that are dropped, they will gain speed
at the same rate as each other even if one is much heavier than the other is.
So if they are dropped from the same height, they will hit the ground at the
same time as each other.This is expressed
scientifically by saying that acceleration due to gravity on the earth?s
surface is constant.Mass has no effect
on the speed at which a trolley travels down a ramp.Skill Area E:
Evaluating EvidenceThe experiments went very well and ran efficiently, thanks
to the plan we had drawn out beforehand. So well, we even had time to conduct
another set of experiments using a light gate and a computer package. This
extra equipment made us sure that our results were accurate and could be
counted on. Thanks to the rapid speed of light, this device is extremely
sensitive and can measure speed to a very fine degree. For our experiment, we
didn?t require it to be as accurate as the system allowed so we rounded the
results off to three significant figures. With our second set of results we
were certain they were reliable and could be counted on. Unfortunately, the
same couldn?t be said for the first set of experiments where we manually timed
the time the trolley took to travel down the ramp. Due to human error and
reaction time, these results could not be relied on completely, but did give us
a rough idea. If we were to conduct the experiment again, I would save time by
just producing results using the computer system with light gate. ??????????? There was
one result that did not fit the pattern, and was too extreme to be our reaction
time. This was the result for 0g on the manually timed weight experiment. It
was suspiciously lower than the others were, and we agreed that it was the fact
that the trolley hit the side wasting its energy on friction. When we noticed the
trolley had hit the side, we decided to take the result anyway just to prove
the point. ??????????? Thankfully,
we had arranged to collect a sensible amount of results, which gave us enough
information to draw a conclusion from. I would not choose to change the amounts
if I conducted the experiment again because we managed to achieve maximum
outcome in the time allotted. ??????????? If I were
to do this experiment again, I would experiment with different surfaces of
ramp. I wasn?t expecting the mass to have any difference on the speed but, even
with the light gate, results showed a slight increase. I assume this was due to
friction and would like to investigate its properties. Also I would use a
trolley than travelled in a straight line! The main problem we found in our
experiment was that the trolley kept swaying to the sides, creating a longer
journey and most of the time hitting the edge. This wasted a lot of time as we
had to conduct the result again. This also could have been due to uneven floor,
so a spirit level may come in handy. ??????????? To extend
this work, we could conduct Galileo type experiments, but take them a step
further. Perhaps, if we had the access to the right equipment, we could drop
weights from different heights in a vacuum (i.e. no air resistance), calculate
the speed using light gates and see if it produces theoretically perfect
results. We could also try eliminating any other opposing forces, such as
friction, by polishing surfaces etc. and noticing if this changes the results. ??????????? To take
the potential/kinetic energy element even further, we could look into elastic
potential energy and see if it works on the same principle as gravitational
potential energy. A simple experiment, such as pulling a trolley back against
an elastic band and letting go to see how far it goes, or what speed it goes at
would be of interest. And we could also look into what parameters effect the
outcome, such as distance elastic is pulled, weight of trolley, type of surface
etc. ??????????? All these
things would help further our progress in this area of physics and help our
understanding of the subject.Bibliography PHYSICS FOR YOU ? Keith Johnson WESTMINSTER COLLEGE RESOURCE PGCE NOTES ? Bev Aldridge FORCES IN ACTION