Which of the following is an effect of applying force?

Applying force to an object results in a change in the object's motion, which can include adjusting its speed. According to Newton's Second Law of Motion, the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass. When force is applied, it can increase or decrease the speed of the object depending on the direction of the force relative to the object's motion.

For instance, if you push a stationary car, you're applying force that changes its speed from zero to something greater than zero. Similarly, if you apply brakes (a force in the opposite direction), you decrease the car's speed. This highlights the direct relationship between force and the motion of objects, making the option related to changing the speed of an object the correct choice.

The other options do not correctly describe the direct effects of applying a force in the context of motion. For instance, creating a vacuum involves different physical principles, and increasing gravitational pull is a matter of mass and distance rather than force application. Reversing temperature does not relate to force and motion either, as temperature is a measure of thermal energy rather than a mechanical effect resulting from force.