(2) When there is ice and snow on the road surface, the road surface becomes smoother and the friction between the road surface and the tire becomes smaller.
The car stops because the tires are subjected to friction from the ground, and the ice on the ground reduces the friction between the ground and the tires, so when braking at this time, the car will slide for a longer distance.
Guess: The more impurities in water, the lower the freezing point of water or mixture.
Reasons: Road maintenance workers often sprinkle a lot of salt on the road surface to avoid the phenomenon of "freezing at night and melting at day", that is, at the same temperature, the melted ice and snow will no longer freeze;
The purpose of dusting and wheel chain is to increase the roughness of the contact surface. The rougher the contact surface, the greater the friction.
(3)① Solution: Let the rectangular iron block have a density of ρ, a height of h and a bottom area of s. 。
Then f = mg = rhovg = rhoshg,
P=Fs=ρsghs=ρhg，
It can be seen that the pressure of a solid cylinder with uniform mass distribution on the desktop has nothing to do with its weight and bottom area, but only with its height and density, so guess 3 is correct. ② Brief experimental steps and judgment methods:
Put three objects gently on the snow;
Observe the depth of an object in the snow,
If they are immersed in the snow at the same depth, it means that they have the same pressure on the snow, that is, the pressure has the same effect, thus proving that conjecture 3 is correct.
③ The known snow density ρ = 0.1g/cm3 =100 kg/m3, and h = 20cm = 0.2m
According to ①, the pressure of the object placed on the ground on the ground is p = fs = rhosghs = rhohg =100 kg/m3× 0.2m = 200 pa.