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Why do I decelerate faster
on my skateboard when I
go over dry concrete
rather than wet?
watch the video to the right
to find out!
First I used the FBD of when I was coasting on my skateboard.
You can see another FBD in my video
By Paxton Swisher
From this FBD we can find that
Sigma Fx = -Ff = ma
and Ff = Fn (mu)
ma = - Fn (mu)
ma = - Fg (mu)
ma = - mg (mu)
a = -g (mu)
Sigma Fy = Fn = Fg
If you watch the video you will find that I used
the equation a = - g(mu) which I just found
and plugged in some average mu s of concrete with rubber. avg. when dry = .7, when wet=.5
a dry = -9.8 (.7) = -6.86 m/s2
a wet = -9.8 (.5) = -4.9 m/s2
This shows how I decelerate faster when the conrete is dry rather than when it is wet.
We have discovered through the video and text
that the reason I decelerate faster on dry
concrete rather than wet concrete is because of the coefficient of kinetic friction. The wet concrete has a smaller mu so it has a smaller deceleration. I hope you have enjoyed this presentation..
NOTE: The friction used in my diagram and equations is not the friction to use when dealing with rolling wheels. With sliding wheels the friction I used would be O.K. but because the wheels of my skateboard were rolling then I had to take into account the kinomatic energy that goes into the rotation of each wheel. because we have not learned this yet I used the friction of sliding instead. Thank you for seeing my presentation.