Tides rise on the sea. why?

Which type of wave can travel without a medium

In all trials, the magnitude of the final velocity for g1 + g2 was less than the magnitude of any initial velocity. as mass increased, what happened to the velocity? the velocity decreased. the velocity increased. the velocity of g1 + g2 could not be measured. the velocity was not affected by the mass increase.

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.