It is very unlikely, according to Questacon science communicator Michelle Cooper.

She and colleague Alison McGregor joined The Canberra Times outside the national science and technology centre in Canberra on Friday afternoon to try out some of the myths and theories commonly heard during heatwaves.

It was 34 degrees at 12.15pm and Ms Cooper tested the temperature of the asphalt underfoot at 71.5 degrees.

But a cracked egg showed no sign of cooking.

The chances of frying an egg on the footpath or on asphalt were very low, Ms Cooper said. ''Asphalt and concrete aren't very good at conducting heat, so when you put the egg on there it actually cools the asphalt very slightly and then it can't get that heat back,'' she said.

Do dark-coloured cars get hotter than light-coloured cars?

Generally, yes.

The women, both members of Questacon's in-house theatre troupe the Excited Particles, parked two cars next to each other in direct sunlight for about 3½ hours, one beige the other dark green.

Proving the importance of never leaving children or pets unattended in cars, by lunchtime Ms Cooper recorded a temperature of 73.2 degrees in the beige car and 80.2 in the darker car. The surface temperatures of the bonnets were 64.8 and 85.8 degrees respectively.

The roof of the dark car was 93.4 degrees. ''The dark car was hotter than the light car mainly because of the way that light reacts with surfaces,'' Ms Cooper said.

''The light and the heat are being absorbed, the darker the surface the more of that is going to be absorbed, the less that's bouncing off, which is why we found such a difference in temperatures between the two cars,'' she said.

A frying pan left in direct sunlight on the dashboard of the beige car reached a surface temperature of 100.5 degrees, hot enough to begin to cook an egg.

Ms Cooper warned that without controls the demonstrations constituted anecdotal evidence only and were not scientifically sound.

At the Australian Open this week tennis player Caroline Wozniacki, a former world No. 1, said the bottom of her water bottle started to melt.

But the CSIRO's Thilak Gunatillake said that while he could not speak to the specifics of the case, the claim was unlikely to be completely accurate.

The research group leader at the science agency's materials, science and engineering division, he said that polyethylene terephthalate or PET was the most commonly used plastic in manufacturing plastic drink bottles like those used to package soft drink.

Dr Gunatillake said most plastic melted at temperatures hotter than 100 degrees and PET plastic bottles melted at 250 degrees.

The heat deflection temperature of PET bottles, when the plastic started to lose its mechanical strength, was 70 degrees, he said.

But Dr Gunatillake said it was possible to observe changes to plastic as it warmed up.

''At about 40 or 50 degrees any of those plastic materials used in water bottles should not melt, but they may get a bit softer. So if you feel the bottle you can see it's actually more flexible than say at a 25 or 30-degree temperature,'' he said.

The ACT government's Emergency Services Agency this week advised Canberra residents to avoid caffeinated drinks during the heatwave, saying that they could cause dehydration.

But, according to a University of Canberra expert, there is no need to skip that morning coffee when hot weather is expected because the link between caffeine and dehydration is a myth.

Associate Professor Kate Pumpa is an accredited exercise physiologist and sports dietitian.

She teaches exercise physiology in the university's department of health.

She said a review completed at the Australian Institute of Sport in 2008 found there was no link between caffeine consumption and dehydration.

''In reality if people aren't drinking other sorts of fluids they're much better off to be drinking coffee or tea than drinking nothing at all, because you will retain some of that fluid, it doesn't dehydrate you,'' she said.