Transcript Motion Analysis

Motion Analysis
• By Leung Ho Fai 6B(35)
•
Siu Long Kan 6B(25), group2
• In this motion, we are going to analysis the
motion of “flying disc” in a projectile path.
How can we analysis it?
• We throw a disc and use a digital camera to
record the motion of the “flying disc” , then
make a v-t graph to find the velocity change
of it.
Velocity-time graph of the
motion of the “flying disc”
Analysis
• For the first 0.9 second, we are getting ready to
throw the disc.
• Before we throw the “flying disc” out. We have to
grab the disc towards our body so that we can
throw it away. This can explain why the velocity
became negative around the first 0.6 second as we
have taken the right hand side to be positive.
• From 0.6 to 0.9 second, the disc has just be thrown
above the horizontal level, so there exists a
positive sign on that instant as the upward motion
is taken to be positive.
Analysis II
• From 0.9 to 1.25 second, the disc keeps
rotating itself below the horizontal level
about a fixed position in a very short period,
so the velocity decreases.
• From 1.25 to 1.5 second, the disc moves
forward in a steady slope of path with a
uniform acceleration.
Conclusion
• This disc-throwing is a counter example since it is
both a projectile and a rotated motion.
• In this case, we consider the projectile motion only.
• In projectile motion, the horizontal velocity is
being unchanged at a fixed value throughout the
whole journey and the vertical velocity is
increasing with required time. At first, the initial
vertical velocity is zero.Applying the equation of
motion, s=usin0+1/2at2, the vertical velocity will
start to increase when the motion is keeping on.
Conclusion II(vertical v)
• However, this example exists the presence of air
resistance. The vertical velocity starts to decrease
rapidly since s=usin0-1/2gt2. As we have taken
downward motion as negative sign, thus it
decrease negatively. Finally, when the air
resistance force reaches its limits and is balanced
by the downward force, net force=mg=ma, free
fall of gravity occurs prove that the v-t graph
during the period of 1.25 to 1.5 second.
Conclusion III(horizontal v)
• It is no longer constant due to air resistance.
This air resistance which is acting upward
increase the speed of the disc, causing the
above graph results.