Assuming all objects are moving with the same velocity, which statement describes the object with the smallest inertia?

A driver continues forward after his car takes a sharp turn.

A bowling ball rolls across a street and into a large soccer field.

A pebble is thrown in space and continues in a straight line.

An avalanche of snow falls down a steep mountain side.

A pebble is thrown in space and continues in a straight line.

Explanation:

Inertia is a property of an object that describes the tendency of the object to resist to any change in its motion.

In other words: if an object has a large inertia and it is moving, it will be more difficult (=a larger force will be required) in order to stop the object (and similarly, if the object is at rest, a large force will be required to put it in motion). Instead, if an object has a small inertia, less force will be required to stop it or to put it in motion.

From the description above, it is clear that the inertia of an object depends on its mass. In particular, for object travelling at the same velocity, the larger the mass, the larger the inertia (since more force is required to change its state of motion).

In the problem, we have 4 objects moving at same velocity:

- Driver

- Bowling ball

- Pebble

- Avalanche

The object with smallest inertia will be the one with smallest mass, therefore the pebble.

A pebble is thrown in space and continues in a straight line.

Explanation:

Inertia is the resistance of a body to change its velocity, this means to change its speed and direction. From this concept we can deduct that the mass of an object is directly related with the inertia, because the more mass, more resistance to change its velocity, or its state of motion. For example, it's way more difficult to move a cow than a dog, due to the mass.

So, a quick way to find the right answer is to look for the object with less mass. Among the options, the pebble has the less mass, so it's the one with the smallest inertia, because the force need to change its state of motion is less than a bowling ball, an avalanche of snow or a driver.

Therefore, the answer is the third one.