• Question: My brother is stronger than me but, if I want too, I can keep him out of my room by just putting my foot against the bottom of the door. How does that work??

    Asked by monkey10 to Mark, Paul, Sarah on 24 Jun 2010 in Categories: .
    • Photo: Paul Roche

      Paul Roche answered on 24 Jun 2010:

      That’s because of friction – your brother has to push your foot across the floor, so he has to overcome the friction of the bottom of your foot as it rubs along the floor – and leverage, as they will be pushing the middle of the door, and your foot is down at the base of the door. If you had a small wooden wedge, you could jam that under the door and he wouldn’t be able to get in at all!

    • Photo: Mark Roberts

      Mark Roberts answered on 24 Jun 2010:

      That’s a question of levers!

      So have you ever used a lever to try and move or lift something – if you have try holding the lever at different places – the closer you are to the point where the lever moves the more force you have to apply to move it – and the further you are the less force

      It’s a really useful property as it allows you to life things that are much heavier with less effort

      So the distance your foot is away from the hinge gives you more power to keep the door shut! You could of course cheat and just use a wooden wedge?

    • Photo: Sarah Bardsley

      Sarah Bardsley answered on 24 Jun 2010:

      Because you have powerful feet!!! Or, more scientifically, because of leverage. Having your foot at the bottom of the door gives you a mechanical advantage. The small effort you put in beats the larger force of your brother because you’re further away from the pivot point. Congratulations!!!

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