Mar 20, James number 5 Mar 10, Mar 12, Thanks for sharing your connection to this Wonder, James! May 11, Are you a crispy chicken? Nov 5, Feb 28, Then you must have really loved this Wonder! Thanks for sharing, Matthew! Oct 26, Have you ever ridden a train, izzay? Or are trains common where you live?
Johnnie Oct 19, Oct 21, Oct 19, We're glad you joined us for this Wonder, izzay! Thank you for leaving a comment! Rockar Oct 17, JAY Oct 24, Oct 25, Izzay Oct 20, Oct 18, Isabel Oct 14, I haven't really rode a real train other than the one at Niabi Zoo in Moline Illinois. Oct 17, Thanks for sharing your connection to this Wonder, Isabel! We bet that was a fun train ride! Oct 14, Ben Oct 17, Thanks for visiting Wonderopolis, kc!
Karter Oct 14, Related Wonders for You to Explore Match its definition: the property created by the space between two objects or points. Word Match Congratulations!
Share results. Play Again Quit. This construction is great for straight tracks. But when a train needs to go around a bend the fact that both wheels are always rotating at the same rate can become a problem. The outside of a curve is slightly longer than the inside, so the wheel on the outside rail actually needs to cover more distance than the wheel on the inside rail.
You can demonstrate this by drawing a train track—consisting of the two rails—with a turn on a piece of paper. Take a measuring tape or string and ruler and measure the length of each line. The outside line of the track should be longer than the inside line. But how can one wheel cover more distance than the other one if they both are rotating at the same rate?
This is where the wheels' geometry comes in. To help the wheels stay on the track their shape is usually slightly conical. This means that the inside of the wheel has a larger circumference than the outside of the wheel.
They also have a flange, or raised edge, on the inner side to prevent the train from falling off the tracks. When a train with slanted wheels turns, centrifugal force pushes the outside wheel to the larger part of the cone and pushes the inside wheel to the smaller part of the cone. As a result when a train is turning it is momentarily running on wheels that are effectively two different sizes.
As the outside wheel's circumference becomes larger it is able to travel a greater distance even though it rotates at the same rate as the smaller inside wheel. The train successfully stays on the tracks! In this activity you will test for yourself how train wheel shapes impact their ability to stay on track. Observations and Results The different cup setups represent different train wheel shape possibilities.
Both cup setups represent a set of slanted train wheels, but the direction in which the wheels are slanted was exactly the opposite. Whereas in the first setup the outer side of the wheel had the larger diameter, it was the reverse in the second cup setup.
The wheel design makes a huge difference in how the wheels behave on a track, as you likely observed. It was probably difficult to keep the first cup assembly on the track. It should have derailed almost every time before it reached the end of the track. No matter how you placed the cups they probably usually fell off the track.
This assembly only stays on the track if it is perfectly centered. But this is almost impossible to accomplish. As soon as the setup is slightly off-center it will derail on its way down the slope. When you off-centered the assembly to the left the part of the cup that is sitting on the left rail had a smaller circumference than the part of the cup that is sitting on the right rail.
Thus the left wheel of the train was smaller than the right wheel of the train. Instead, you need to just get one car moving at a time - this is why there is space between the couplings. I think there is some interesting physics here. In particular, there is something curious about the difference between static and kinetic friction. First, let me make some observations and assumptions. The train has a big engine in it.
This engine makes the wheels turn to pull the rest of the cars. If we consider the train and wheels as the system, the force that changes its momentum is the static friction force between the wheels and the rail. Yes, right. What about the cars? They also have wheels. However, these are not driving wheels, they just roll but they also have friction. I will assume that the frictional force is in the axle of the wheels. For these rolling cars, the friction is kinetic friction and not static.
What is the difference between kinetic and static friction? Static friction is the model for the frictional force between two surfaces that are at rest relative to each other. This would be the case of the engine car's wheels.
Even though the wheels are rolling, the point of contact with the rails is at rest with respect to these rails. Kinetic friction is the model to use when the two surfaces are moving relative to each other - like the car's axle and the rest of the car. Consider a train in which all the cars have stretched couplings.
Why do we rarely get sick in a train? Why do iron-wheeled metros and rubber-tyred metros exist? How does a train work? How does a tram operate without overhead wires? How does a metro work without a driver?
How does coupling between two trains work?
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