Use studded/spiked tires, or use snow chains for bikes. Or have someone walk ahead and spread sand on the susrface.
friction
Friction which causes heat.
Either the friction or density of the snow.
gravityGRAVITY
Friction and a good grip.
unless you have chains or studs it would be 0 friction
Pressure certainly does increase in a water line going down hill. This is because the weight of the water pulls it.
Friction increases or decreases based on the surface changes. If a box were sliding down a smooth hill that suddenly becomes quite rough, then friction would increase. It would be the same vice versa for decreasing friction.
Friction and air resistance
if there is friction on the hill it will slow you down
idk
The friction is rolling.