popping an ollie physics of cool tricks

[theorchardz]

Hi, thanks for this experiment. We completed all of the steps and are analyzing results. Physics is a bit complicated and we are trying to understand what happened. For our version we used one 50kg skater traveling a horizontal run of 180 inches on the same board each time at speeds of 2 seconds 3 seconds then 4 seconds from start to pop ollie. We did 12 trials and we found the skater went highest stopped or standing at 0,0 and then progressively farther faster with the ollie getting lower and lower measuring lowest at the fastest speed. How is it explained what happens when the skater goes south in the horizontal run and changes his body mass to face west to pop that ollie, does it slow the board? And exactly why does the ollie "get lower" Did it really or did it just appear that way? Does horizontal speed affect the vertical jump or did it just carry it further until mass and gravity pulled it down? Thanks again, it was definitely a fun one to do as we have many skaters in our hood.... so much to share with them on tricks!

[deleted-71709]

Hi!

It sounds like you are really having some fun with physics.

I must admit, I'm not a skateboarder, nor have I ever been one. But I do know about physics. I spent a little time reading up on our description of this experiment, so I could figure out your questions. Here's what I can tell you.

From what I do know about skate boarding, and having watched the video in our project description, I can't figure out why your rider "goes south in the horizontal run and changes his body mass to face west to pop that ollie", but that doesn't make any difference. It is the mass of the rider, not the direction he/she is facing that makes a difference. So, to answer your question, no changing position on the board does not affect the speed.

Regarding your question, "Did it really or did it just appear that way? (get lower)". You should have the data to answer that yourself. If you performed your experiment in front of a wall, with the height measuring lines marked on it per the instructions, and if you took videos, or even still camera shots, you will have the data to answer your question. If the images indicate the height was lower, then it was.

Why would this happen? First of all, the speed does affect the distance traveled during the ollie because of the energy stored in the combination of the rider and the board. You will find if you have a heavier rider, traveling at the same speed as a lighter rider, the heavier rider will go farther. That's because there is more kinetic energy stored in the mass of the heavier rider/board combination. Kinetic energy is mass time speed squared.

Now, about the height. In theory, all ollies should have been the same height. That is because the height of the ollie is determined by the energy put into the rider and the board by the rider. IF the rider puts the same effort into his/her jump, and kicks the tail of the board with the same effort every time, the rider and the board will jump the same height every time. I already told you I'm not a skate boarder, but I think what could likely be happening is that at higher speeds, the rider may not be as fearless and may not put as much energy into the jump as at lower speeds. Does that sound possible?

I'm glad you had a good time with this one.

[theorchardz]

Hi thanks for the reply.
regarding physics to your post would it be that a horizontal speed does not affect vertical jump? a jump is only as good as ajump?
a physics person mentioned it could be explained that the jump was affected due to vertices, like a ball on a moving bus? how? or not correct?
can an equation be written for the 50kg skater traveling 180 inches at speeds of 2, 3, and 4 seconds?
for future experiments i noticed that the world record olliers actually zigzagged or pumped to the obstacle, how does that affect their ability to jump? how about using a ramp?
thanks.

[kgudger]

From your description, it sounds like the horizontal speed does affect the vertical height - that it has a negative correlation. There could be many reasons for this. Can you view your video you took at a slower speed? If you can stretch it out, maybe you could analyze what was going on at the base of the board when the kick occurs? If you need more video of just the kick portion, maybe you could redo some of the experiments and zoom in on this part of the board.

The equation you might want is the one already mentioned - for kinetic energy. KE = 1/2 m * v(squared). You can look up kinetic energy in a search engine to get more information. It would be best to use all metric measurements. You already have the weight in kg, but you need to convert the 180 inches into meters to get a velocity in meters per second.

You other questions about future experiments are all interesting, and can be included in your report.
Keith

[theorchardz]

Hi- when you mention a "negative" response can you write what you think could have happened? What should I look for in the video replays?
Thanks.

[deleted-71588]

From your description, it sounds like the horizontal speed does affect the vertical height - that it has a negative correlation.

I suspect "negative correlation" might be better described as "inverse correlation" in this case based on your observations. The faster the horizontal speed, the lower the vertical height.

what you think could have happened? What should I look for in the video replays?

Precisely what you are looking for is "unknown". Our best guess is there is something different besides the speed. Is the skate boarder's weight more forward or backward, higher or lower, is there a shift in weight that is faster or slower? Look at the ankles, knees, waist, back, head, shoulders, elbows, hands and the angle the wheels hit the ramp, angle of the board when it starts onto the ramp and leaves the ramp, where on the ramp are these points for possible clues.

From a skier's perspective doing arials, if the person doesn't keep straight like a pencil trough the take off, they will get compressed into a ball and loose vertical acceleration and not go as high. I'm not sure if this applies to skate boarding ramps as well. The faster the skier is going to start with, the more force trying to compress the skier and the harder it is to keep straight to convert the horizontal speed into vertical acceleration.