Why do planes look so slow when we look at them from the ground?

Difficulty: Summiteer (Level 2)

A passenger jet flies at about 925km/h once it is high in the air. That is nearly nine times faster than a car might typically be driving on the road. So why does a flying plane look like it is just inching slowly across the sky?

In reality, looks can deceive us about how fast an object is moving.

Gauging a plane’s speed

If you watch a plane accelerating towards take-off, it appears to be moving quickly. It is not until the plane is high in the air that it appears to be moving slowly.

When there are no clouds in the sky, we have no other objects to compare the plane’s speed with. It is just moving against a giant background of the blue sky. This can make it very hard to understand how fast a plane moves.

Because the plane is far away, moving across our field of vision takes longer as compared to an object close to us. This further creates the illusion that the aircraft is moving more slowly than it is.

Passenger’s perception on the plane

Sitting on a plane doesn’t feel like we are moving that fast because we are moving at the same speed, too. This can make it difficult to perceive our speed compared to the ground. This is the same reason it can be hard to tell that you are driving quickly on a road surrounded by empty fields.

However, you can understand how fast you are moving in a couple of ways.

Can you see the plane’s shadow on the ground? It can give you an idea of how fast the plane moves relative to the ground. If you are lucky enough to spot it, you will be amazed at how quickly the plane’s shadow passes over buildings and roads.

Another way to understand how fast you are moving is to note how fast the clouds move over the plane’s wing. This gives you another way to “see” or perceive your speed. Remember that clouds aren’t typically stationary, but they move slowly compared to planes.

Although it can be challenging to see how fast a plane is moving, you can use reference points to gain perspective.

Use the puzzle below to test your knowledge of the vocabulary words in the story.

Sample answers

• Stop and think: What is one reason that a plane looks like it is moving slowly when we are watching it from the ground? This is because we have no objects in the sky to compare it to. / This is because it takes longer for it to move across our field of vision compared to an object that is close to us.

• Consider: How could spotting the plane’s shadow help you perceive its speed? The plane’s shadow moves very quickly over buildings and roads.

• Answer this: Why are clouds often moving over a plane’s wing? The clouds are moving more slowly than the plane is.