Moment / CG question regarding a bicycle

[JohnNova]

Hi,

Lets say that we have a 2 wheel bicycle riding at 2m/s. The weight distribution on this bicycle implies that the front wheel is exerting a total of 400N on the ground, whilst the back is exerting 560N.

How would I work out whether at this speed if I were to lock up the front brake, provided it didn’t skid, the rear of the bicycle would lift off the ground?

How would I work out the moment force… Where would I be measuring to… where would I define the CG (centre of gravity) to be?

I am working on an investigation and ANY help would be greatly appreciated!

Thanks in advance.

 

[civil_dude]

You need to find the moment about the front axle, and assume a static coefficient of friction. The CG can be found by finding the equal moment the total weight produced compared to just the rear, summing them about the front.

 

[kyle8921]

I would approach this question by using the principles of mechanics and the laws of motion. First, I would calculate the total weight of the bicycle by adding the forces exerted by the front and back wheels (400N + 560N = 960N). This weight would act as the downward force on the bicycle, with the center of gravity located somewhere along the frame of the bike.

Next, I would consider the forces acting on the bike when the front brake is locked. In this scenario, the only force acting on the front wheel would be the friction force from the ground, while the back wheel would continue to exert its full force of 560N. This would create a moment force on the bike, causing it to rotate around its center of gravity.

To determine whether the rear of the bike would lift off the ground, I would need to calculate the moment force and compare it to the moment of the weight of the bike. The moment force can be calculated by multiplying the force exerted by the back wheel (560N) by the distance from the center of gravity to the back wheel. This distance can be estimated by measuring the length of the bike frame from the front wheel to the center of gravity.

If the calculated moment force is greater than the moment of the weight of the bike, then the rear of the bike would lift off the ground. This would indicate that the bike is not stable in this scenario and the rider should be cautious when applying the front brake at this speed.

In summary, to determine the moment force and the stability of the bike in this scenario, you would need to calculate the weight of the bike, the distance from the center of gravity to the back wheel, and compare the moment force to the moment of the weight. I hope this helps with your investigation. Best of luck!