Asap how does the acceleration due to gravity at the surface of a planet change if the planet's radius is doubled?

Which of the following is not am example of a polymer? protein nylon kevlar concreta

How is sound energy produced a. vibrating objects b. objects being heated c. temperature differences d. stationary objects

Would it be correct to say the doppler effect is the apparent change in the speed of a wave due to the motion of the source? be sure to fully explain your position using at least 3 complete content related sentences.