Video+Explanations

Emma Hersh Train Surfing Physics Explanation When the video starts, the train isn't moving, so neither am I. The forces acting on me are balanced, the gravity acting on my body is holding me to the ground and the train to the rails. At the same time there are forces acting on me from the front and from the back that keep me standing straight up. As the video progresses, the train starts to accelerate forward so the force acting on the front of me was more powerful which made me move backwards. Once the train is finished accelerating, it begins moving at a constant speed again, which makes the forces acting on me unequal again. I have to shift my weight again to stay balanced and standing straight up. Toward the end of the movie, the train starts to negatively accelerate which makes the forces acting on my back bigger than the one on my front, so I start to move forward. At the very end of the video, the train stops at the station, and having moved with the train this whole time, my body suddenly jerks, having to rebalance myself so I don't fall.

TJ Nicolella Bus Surfing Physics Explanation Throughout the video, the bus is constantly accelerating then slowing down, or negatively accelerating. The two student passengers in the video are consistently holding onto something, anything they can in order to stay standing because there is an unbalanced force pushing them backwards when the bus accelerates. When the bus is coming to a halt at a red light (while accelerating negatively) there is again an unequal force being put on the passengers that shows more so on those who are standing. When the bus is slowing, the force on the passengers backs is more powerful than that being forced onto the front of their body, causing them to jolt forward (more so if the passenger is not holding onto a railing). Passengers on a Septa bus are able to stand straight up on the bus because of the equal amount of force on all sides of their body. This changes, however when the bus starts to accelerate or negatively accelerate. As the bus moves, the passenger and bus are no longer in a state of uniform motion and the passenger will jolt backward if they are not holding onto the handrails. When the bus is accelerating, it is doing so faster than the passenger ca using them to move to the back of the bus or jerk backwards but they stop moving backwards when the transport comes to a halt because the two parties are then in a state of uniform motion. Passengers that are standing will often times spread their legs a bit farther than shoulder length to evenly spread their weight and therefore stay balanced (especially if they are not holding onto anything). Along with friction caused by ones feet interacting with the floor of the bus, evenly placed body weight can keep the passenger afoot when sharp turns or sudden stops are made by the bus driver. In the case of my video, the two student passengers are holding onto every object that makes them feel stable and do not feel the need to spread their feet apart to stay standing. What will happen in most cases of sharp turns is a falling passenger because as the bus turns to one direction or another, the passenger will lean or tilt to the opposite side the bus is turning without fail. This happens because as the bus turns, inertia still makes your body move in the direction that the bus was moving in before it turned, sharply or otherwise. This movement is also very apparent in sitting passengers that will shift in the opposite direction that the bus is turning because of the same reason.

Daniel Mambu:

This is a video of me in the trolley from 13th street to 30th street. What I was trying to study while doing this video was how steadier you are standing with your hand straight up on the roof of a trolley then standing holding the pole. My guess of what would happen was that I would be steadier while pushing against the roof then holding the pole. When holding the pole the forces acting on you are earth (aka gravity), Floor, and fraction. Gravity is the downward pull or keeping you on the ground, the floor of the trolley is the upward force pushing you up, and friction is the force that is pushing against the pushing force or keeping you from sliding. There is fraction between your feet and the ground as the trolley accelerates it creates an unbalance force because there’s no force balancing friction. As you stand the forces of gravity and the floor are balance or at rest. As the train accelerates right you lean left making you unbalance causing you to adjust. Friction is what pushes against the accelerating force keeping you from sliding left. As you hold the pole this occurred. But this is only occurring on the floor. As I sat in the trolley one day I watched a man come in the trolley I was in. It was crowded and with on poles to hold. When he realized there was no pole or anything to support him he reached up for the roof of the trolley. I watched closely thinking he would easily fall forward or backward but it never happened. The interesting thing about this was he seemed more stable then every body else. That’s how I got the idea or question to figure out which was better and why it was better. So I tried it and this is what I think happened. Now you already know as you stand on the trolley that’s not moving the forces are balance and there’s fraction between your feet and the floor. Let’s just say you are at rest and are in a constant motion. As the trolley accelerated you became unbalanced because your motion resisted the change. Same thing happened when the trolley stopped. Your body kept its motion. I figure by pushing up against the roof of the trolley you are the n creating both friction above with your hands and the roof. By doing this you now have two form of friction. You have both frictions above and below. This causes a steadier motion. Now gravity is pulling you to the floor and the floor is pushing you up. This happens below you. When pushing up you are also creating the same force. Like gravity your hands are pushing you to the roof and the roof is pushing back. This levels out the friction. For example when you have a book on a table and push it that book moves. But what happens when you put and upside down table above the book on the table and try to push the book. You need a great amount of force to move the book just a little. Same thing if you push up against the roof on the trolley. The greater the push the more stable you will be. That’s what happened in the video. When the video started the train was moving but in this whole video the trolley accelerated 3 time and decelerated 4 time. There only a little effect and it was because of the tracks.

Sites I used: 1: comPADRE,. (1996). //The physic classroom//. Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l2a.cfm 2: comPADRE, Initials. (1996). //The physic classroom//. Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l1a.cfm 3: comPADRE, Initials. (1996). //The physic classroom//. Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l4a.cfm