Bicycle Helmet Physics - Momentum Calculations

AI Thread Summary
Energy is defined as force multiplied by distance, and the impact force from a helmet during a fall is minimal due to the helmet's thickness. The calculations suggest that a collision at 20 km/h with a helmet is comparable to a 2.8 km/h impact without one, highlighting the helmet's protective effectiveness. The discussion acknowledges that while the force isn't linear due to helmet distortion, a reliable time figure of 6 ms for helmet protection is used, although an arbitrary 1 ms value may skew results. Research indicates that the human skull is about 6.35 mm thick, while helmet foam is 20 mm, suggesting that the skull provides less time for deceleration compared to the helmet. Overall, the analysis emphasizes the importance of understanding the physics behind helmet design to illustrate their protective benefits.
yowatup
Messages
8
Reaction score
0
edit
 
Last edited:
Physics news on Phys.org
Energy is force x distance, so that force acting over the distance of the thickness of the helmet isn't very much. Remember also that KE is velocity^2 so 30->40km/h is almost a doubling of en ergy.
 
Right, the wikipedia statement regards energy.

That aside, my calculations of force are sound? That with a helmet, hitting the the ground (or another object) at 20km/h, is roughly equivalent to hitting the ground at 2.8km/h without a helmet?
 
Seems reasonable, it's hard to know the time an the force isn't necessarily linear as the helmet distorts - but I wear one!
 
I'm glad that the calculations appear to be in order, despite the baffling conclusion that 20km/h(w helmet)=2.8km/h(w.o helmet).

You're right about the force not being necessarily linear, but I think I just need something simple to illustrate the effectiveness of helmets.

While I can reliably source the time figure of 6ms afforded by helmets, I think the arbitrary time value I added of 1ms probably skews the data quite a bit. I just don't know how else the comparative analysis would work. I can't calculate the acceleration if I just use the 6ms figure (since t=0 w/o helmet then). The obvious solution is to increase the time that the skull affords, but I really am not sure what number to decide on.
 
Okay, so I did some research and have found that the human skull is roughly 1/4" = 6.35mm thick. Helmet foam on the other hand is 20mm. So I think I can reasonably conclude that the time allowance afforded by the skull is 1/3 of the helmet foam. That is, if it's distance that is the operative variable here that extends time of deceleration; since the human skull is surely stronger, that just means it absorbs more force but doesn't really affect the time.
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Back
Top