Examples of Inertia

, Staff Writer
Updated November 7, 2020
Balls rolling down ramp inertia example
    Balls rolling down ramp inertia example
    K3 / Getty Images

Inertia was best explained by Sir Isaac Newton in his first law of motion. Basically, the law of motion states that an object at rest stays at rest, and an object in motion continues in motion until an external force acts on it. Examine several examples of inertia.

Law of Inertia

When it comes to laws of motion, inertia is one of the greats. Inertia resists change in motion. Objects want to stay in rest or motion unless an outside force causes a change. For example, if you roll a ball, it will continue rolling unless friction or something else stops it by force. You can also think about the way that your body keeps moving forward when you hit the brake on your bike. Inertia comes in different types, check them out.

Types of Inertia

In inertia, there isn’t just one type. Instead, you’ll find three different types of inertia including:

  • Inertia of rest - An object stays where it is placed, and it will stay there until you or something else moves it. (i.e. Dust particles stay at rest until you shake a carpet.)
  • Inertia of motion - An object will continue at the same speed until a force acts on it. (i.e. Body going forward when a car stops.)
  • Inertia of direction - An object will stay moving in the same direction unless a force acts on it. (i.e. One's body movement to the side when a car makes a sharp turn.)

Reading about inertia is great but to understand one of Newton’s laws of motion, you’ll want to look at examples.


Inertia of Rest Examples

Now that you know what inertia of rest is, explore several examples.

  • If pulled quickly, a tablecloth can be removed from underneath the dishes. The dishes have the tendency to remain still as long as the friction from the movement of the tablecloth is not too great.
  • If a stopped car is hit by a moving car from behind, the passengers inside may experience whiplash as a result of the body moving forward but the head lagging behind. The head is experiencing inertia.
  • A balloon in a car will appear to move when the car moves forward, but the balloon is actually attempting to stay in the place it was, it is only the car that is moving.
  • When a car is abruptly accelerated, drivers and passengers may feel as though their bodies are moving backward. In reality, inertia is making the body want to stay in place as the car moves forward.
  • If an index card is placed on top of a glass with a penny on top of it, the index card can be quickly removed while the penny falls straight into the glass, as the penny is demonstrating inertia.
  • When pulling a Band-Aid off, it is better to pull it fast. Your skin will remain at rest due to inertia, and the force pulls the Band-Aid off.

Inertia of Motion Examples

Objects in motion stay in motion or want to, just like these examples.

  • Seat belts tighten in a car when it stops quickly.
  • Men in space find it more difficult to stop moving because of a lack of gravity acting against them.
  • When playing football, a player is tackled, and his head hits the ground. The impact stops his skull, but his brain continues to move and hit the inside of his skull. His brain is showing inertia.
  • If one drove a car directly into a brick wall, the car would stop because of the force exerted upon it by the wall. However, the driver requires a force to stop his body from moving, such as a seatbelt. Otherwise, inertia will cause his body to continue moving at the original speed until his body is acted upon by some force.
  • When a baseball is thrown, it will continue to move forward until acted upon by gravity. The greater the force of the throw, the harder it is for gravity to act upon it.
  • A hockey puck will continue to slide across the ice until acted upon by an outside force.
  • When pedaling a bicycle, if you stop pedaling, then the bike continues going until friction or gravity slows it down.
  • A car that is moving will continue, even if you switch the engine off.
  • If a ball is on a slanted surface and you let go, gravity will make it roll down the slope. It has inertia, and if there is a level area at the bottom of the slope, it will continue moving.
  • When entering a building through a rotating door, inertia will allow the door to hit you in the back if you don't get out of the way.
  • If you are rolling a cart with something on top and you hit something that makes the cart stop, what is on top may fall off.
  • It is harder to stop a big vehicle, like a bus, than a smaller vehicle, like a motorcycle. There is more inertia with the larger object.
  • A concussion occurs because your brain is still moving while the outside skull is stopped. This is what causes the injury.
  • If you are on a train and the train is moving at a constant speed, a toy tossed into the air will go straight up and then come down. This is because the toy has inertia like the train and you.
  • If a car is moving forward it will continue to move forward unless friction or the brakes interfere with its movement.

Inertia of Direction

View how objects stay in the same direction unless another force is applied. Examine examples of inertia of direction.

  • Hovercraft can be a challenge to manipulate because, unlike cars, they do not have the same level of friction, so inertia causes the hovercraft to want to continue in its same direction without stopping or turning.
  • Abruptly stopping a cart with an object on top causes the object on top to fall off. Inertia causes this by making the object want to continue moving in the direction that it was.
  • If you jump from a car or bus that is moving, your body is still moving in the direction of the vehicle. When your feet hit the ground, the grounds act on your feet and they stop moving. You will fall because the upper part of your body didn't stop, and you will fall in the direction you were moving.
  • When you stir coffee or tea and stop, the swirling motion continues due to inertia.
  • Objects that establish orbit around the earth, such as satellites, continue on their trajectory due to inertia.
  • If you throw a rock straight up, it will not vary from its direction.
  • Inertia enables ice skaters to glide on the ice in a straight line.
  • If the wind is blowing, a tree's branches are moving. A piece of ripe fruit that falls from the tree will fall in the direction the wind is moving because of inertia.
  • Space probes are launched to get past the Earth's atmosphere. Then, they coast due to inertia.

Understanding Inertia

See if you can recognize inertia when it occurs over the course of your day. You might be surprised at how much you notice moments of inertia in your life. If you’re geeked about scientific principles, try out examples of gas to solid.