What is the force that acts on an object and opposes its motion called?frictionthermal energyinertia

The force that acts on an object and opposes its motion is called friction. Friction is a resistive force that occurs when two surfaces come into contact with each other. It acts in the opposite direction to the movement of the object, thus slowing it down or preventing it from moving. There are different types of friction, including static friction (which prevents motion), kinetic friction (which acts on moving objects), and rolling friction (which occurs when an object rolls over a surface).

In contrast, thermal energy refers to the internal energy of an object due to the motion of its particles, and inertia is the resistance of an object to change its state of motion. Hence, the correct answer to the question is "friction."