Please help urgent !!! How does an instant cold pack get cold so quickly?

Why is the melting of ice a physical change ?

The famous scientist galileo galilei did several experiments with sloping planes, which he rolled metal balls down so that he could study motion. by changing the slope, he could study how the speed at which the ball rolled was affected. what was the independent variable in galileo's experiment? a. the speed of the ball b. the slope of the plane c. whether the ball moved d. what the ball was made of

How might this scientific phenomena be explained? a paper clip floats on water.