UNIKORN INC.
WELCOME TO MAGIC LAND
Wheelchair 101
Here are the physics behind wheelchairs
Overall:
The are two sets of wheels, the front two smaller ones and the back larger ones. The front two smaller ones are the wheels that allow the wheelchair to turn left right or go backwards or forwards. Because the front two wheels are in free rotation and have a bent as shown in the picture, they will be facing parallel to the way the wheelchair is going, and because their in free rotation, it allows the person to maneuver to the destination they want. The back two larger wheels are the wheels that the person physically uses to move themselves using the handrim, the place where the person grabs. The rear wheels are locked in place, but can turn clockwise or counterclockwise, depending which way the person needs to go.
If the left wheel is stopped, and the right one turns the wheelchair will turn left, if the right one is stopped and the left is turning it will turn right. And because the handrim is closer to the outside than the inside, the person has more torque than if they were to use the handrim near the center of the wheel. Also because the radius of the rear wheel is large, it means for every one rotation, the distance traveled would be much greater than if the radius of the wheel was small. This ingenious design allows people who are injured, or sadly have little or no ability to use their legs, to move around wherever they want.
Math:
The reason why the torque is greater at the outside of the handrim rather than the center of the handrim is because according to this equation torque=force x radius, the person applies the same force if it was near the center or on the outside, however because the radius is greater than it would be at the center, the torque is great. As shown in the math below:
T=f*r
Force = 10 N
Radius #1 = .05 m
Radius #2 = .25 m
Torque for Radius #1 = 10 N*.05 m
Torque for Radius #1 = .5 Nm
Torque for Radius #2 = 10 N *.25 m
Torque for Radius #2 =2.5Nm
As the above math shows, the force applied to the spinning wheel is the same, however the radius changes, and because the handrim has a bigger radius than if it was at the center, the person has a bigger torque pushing on the wheel rather than if it was a smaller radius.
The reason why the rear wheels are bigger is because for every one revolution it would travel a greater distance than if it was a smaller radius. According to the circumference equation, 2Ï€r, as radius increases so does the circumference. The circumference tells the distance the wheel would travel for every one revolution. Or as the example below will show, the circumference of a bigger radius is bigger than if it were smaller.
Circumference=2Ï€r
Radius #1 = .05 m
Radius #2 = .25 m
Circumference for Radius #1 = 2Ï€*.05
Circumference for Radius #1 =0.31415926535 m
Circumference for Radius #2 = 1.57079632679 m