Why do you heat a bottle of mayonaise when its difficult to open?

[kampai]

could anyone try to explain these following? thanks in advance..

1. why do you heat a bottle of mayonaise when its difficult to open?

2. if an engine of a car overheated why is it that it is advisable that you pour water in its radiator slowly with its engine running?

3. why is it there are gaps left on a railroad track instead of just welding them together?

 

[dx]

Not sure about 2, but 1 and 3 have to do with thermal expansion(try to see how and post your thoughts)

 

[daveb]

You pour water slowly with the engine running because if you did it all of a sudden the engine block might crack due to differences in thermal expansion/contraction.

 

[opee5230]

daveb is right. however, I'd like to say for practical purposes, should you find yourself having radiator issues, the best thing to do is wait for the engine to completely cool and then just add the water. there's even less risk of cracking the block that way. As far as the other two, perhaps your instructor requires more detail: The mayonase lid is metal and expands much more rapidly under heat than does the glass jar : lid bigger than Jar--> lid comes off easier. (2) the gaps in the railroad tracks allow the rails to expand without warping and buckling when the metal's temperature rises in the sunlight/climate change, etc.