Scientist explains why trolleys become harder to steer when you leave the shop


Have you ever noticed that as you’re walking around the supermarket, pushing your trolley, it turns smoothly around each aisle, no matter how much stuff you put in it.

But once you’ve paid, bagged up your shopping and head out of the store towards your car – things start to get a little more difficult.

You find it harder to keep control of the trolley and steer it in the direction of your parking space.

Why is that?!

Well, you don’t have to wonder why anymore, as a scientist has attempted to provide a reasonable explanation for this in a podcast.

Speaking on Science with Dr Karl last Thursday, Dr Karl Kruszelnicki answered a question from a listener named Lewis.

Lewis said: “I was out doing the morning shop with a fully loaded trolley this morning.

“Pushing it around the shop was fine, but then as I soon as I got to the car park, I felt as though I had to walk it at a 45-degree angle to keep it straight. Is there any reason for that?”

Dr Karl initially admitted he didn’t know the answer, but the pair eventually worked it out together – it’s all to do with the angle of the ground.

The expert replied: “You’re so observant as that is so true.

‘It is because, inside the shopping centre, the ground is dead flat, whereas outside, almost certainly it is angled to allow water to drain off to where it needs to be.”

He continued to say: “There would only be a half or one-degree tilt that you wouldn’t notice with a naked eye when you were without a trolley, but the trolley would pick it up.”

Another caller on the show later confirmed that this was the case because car parks are angled so that rainwater drains off and doesn’t flood.

So there you have it folks!