Explain why adding oil to the moving parts of a machine can increase its efficiency

Selma made a diagram to compare convection and radiation. which label belongs in the area marked x? must involve temperature differences between substances or objects only occurs when molecules are in direct contact involves the movement of fluids based on density differences can occur where there is little or no matter

Explain why electric current cannot exist if a current doesn't have a voltage source.

Will mark as brainliest how does a catapult increase the trajectory of an object? ps. answer as if u were a 5th grader