# inertia

## inertia and mass

The inertia of an object depends on its mass. Objects with greater mass also have greater inertia. It would be easier for Lauren to push just one of her cousins on her skateboard than both of them. With just one twin, there would be only about half as much mass on the skateboard, so there would be less inertia to overcome. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL:

## overcoming inertia

To change the motion of an object, inertia must be overcome by an unbalanced force acting on the object. The unbalanced force that starts Laurens cousins rolling along on the skateboard is applied by Lauren when she gives it a push. Once an object starts moving, inertia keeps it moving without any additional force being applied. In fact, it wont stop moving unless another unbalanced force opposes its motion. For example, Lauren can stop the rolling skateboard by moving to the other end and pushing in the opposite direction. Q: What if Lauren didnt stop the skateboard in this way? If it remained on a smooth, flat surface, would it just keep rolling forever? A: The inertia of the moving skateboard would keep it rolling forever if no other unbalanced force opposed its motion. However, another unbalanced force does act on the skateboard Q: What other force is acting on the skateboard? A: The other force is rolling friction between the skateboards wheels and the ground. The force of friction opposes the motion of the rolling skateboard and would eventually bring it to a stop without any help from Lauren. Friction opposes the motion of all moving objects, solike the skateboardall moving objects eventually stop moving even if no other forces oppose their motion. Later that day, Jonathan rode his skateboard and did some jumps. You can see him in the picture 1.2. When hes in the air, there is no rolling friction between his wheels and the ground, but another unbalanced force is acting on the skateboard and changing its motion. Q: What force is acting on the skateboard when it is in the air above the ground? And how will this force change the skateboards motion? A: The force of gravity is acting on the skateboard. It will pull the skateboard back down to the ground. Once its on the ground, friction will slow its motion.

## what is inertia

Inertia is the tendency of an object to resist a change in its motion. All objects have inertia, whether they are stationary or moving. Inertia explains Newtons first law of motion, which states that an object at rest will remain at rest and an object in motion will stay in motion unless it is acted on by an unbalanced force. Thats why Newtons first law of motion is sometimes called the law of inertia. Q: You probably dont realize it, but you experience inertia all the time, and you dont have to ride a skateboard. For example, think about what happens when you are riding in a car that stops suddenly. Your body moves forward on the seat and strains against the seat belt. Why does this happen? A: The brakes stop the car but not your body, so your body keeps moving forward because of inertia.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

only moving objects have inertia.

``````a. true

-->  b. false
``````

newtons first law of motion is also called the law of inertia.

``````-->  a. true

b. false
``````

which object has the greatest inertia?

``````a) 5-kg rock

b) 6-kg box of feathers

c) 7-kg bag of groceries

-->  d) 8-kg bowling ball
``````

once an object starts moving, inertia keeps it moving without any additional force being applied to the object.

``````-->  a. true

b. false
``````

## diagram questions

No diagram questions associated with this lesson