# Thermal Physics: Ice skating temperatures

by H.fulls
Tags: physics, skating, temperatures, thermal
 P: 18 1. The problem statement, all variables and given/known data It is said that good ice skating only occurs when the ice below the skates melts. Using the Clausius-Clapeyron equation, estimate the coldest temperature at which good ice skating can occur. (Water expands 9% on freezing, Latent heat of ice melting is 334 kJ/Kg, the contact area is 1mm by 5cm and the skater weighs 70kg, water has a molar mass of 18g) 2. Relevant equations $\frac{dp}{dT}$ = $\frac{L}{T(V_{2}-V_{1})}$ or I think rearranged like this $p_{0}$-p = $\frac{L}{\DeltaV}$ ln$\frac{T_{0}}{T}$ 3. The attempt at a solution I have found the pressure exerted as 1.372 x $10^{7}$ kg/$m^{2}$ I realise that we want the ice to be melting.. so 273k at this pressure, so I need to find the temperature at normal room pressure of 101 KPa. However I dont know what to use for the volume?
HW Helper
Thanks
P: 4,845
 Quote by H.fulls $\frac{dp}{dT}$ = $\frac{L}{T(V_{2}-V_{1})}$ or I think rearranged like this $p_{0}$-p = $\frac{L}{\Delta V}$ ln$\frac{T_{0}}{T}$
Often, you can get an accurate enough answer without integrating by treating the right hand side of the Claussius-Clapeyron equation as constant over the temperature changes involved. Then you can just write it as

$\frac{\Delta p}{\Delta T}$ ≈ $\frac{L}{T(V_{2}-V_{1})}$
 I have found the pressure exerted as 1.372 x $10^{7}$ kg/$m^{2}$
This looks correct except for how you expressed the units. Pressure is force per unit area, not mass per unit area.
 However I dont know what to use for the volume?
The volumes ##V_1## and ##V_2## are "specific" volumes (i.e., volumes per kg of material). Note that water is odd in that the ##V_1## (for ice) is greater than ##V_2## (for liquid water).
 P: 2 ... and the answer comes out around -1.0 degree ??
 HW Helper Thanks P: 4,845 Thermal Physics: Ice skating temperatures Yes..which debunks the idea that ice skates slide well on ice due to pressure causing the ice to melt and become slippery. See http://www.nytimes.com/2006/02/21/sc...pagewanted=all
 P: 2 Agreed ... it is far more complex.

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