Skip to main content
Physics

Return to Question

edited tags
Source Link
Qmechanic ♦
Qmechanic ♦
  • 213k
  • 48
  • 590
  • 2.3k

This is a question I've had for several years but never had the knowledge to calculate myself. Please keep in mind I don't have much background in physics (learned some on middle school I guess...), but I'd still love a thorough answer and I'll do the research further needed to understand it.

Years ago, I was told that the force applied on my back while brushing my teeth leaning is about a 2000kg, and putting a hand down on the sink would make this force become 0. I found this very weird but lately I started doing some work with motors and found the force of torque, so this feels a little more possible but still kinda wrong.

So let's get to it. Assuming I lean forward while brushing, my weight would have some force on the pivot point of my back.

Let's assume that pivot point is 95cm above the ground, and the top of my head is 171cm above the ground. This gives us a total of 76cm from the top to the pivot point.

Let's also assume that the weight above the pivot point is 55kg and that it's spread equally throughout the height.

We'll also assume that the leaning angle is 25° from the position where I'm standing straight.

How can I calculate the torque (or whatever units of measurement would be appropriate here) applied on that pivot point?

Bonus: How can I calculate the torque applied when putting a hand down? You are welcome to assume anything here since I don't even know what variables would be needed for such a calculation.

Thanks a lot!

This is a question I've had for several years but never had the knowledge to calculate myself. Please keep in mind I don't have much background in physics (learned some on middle school I guess...), but I'd still love a thorough answer and I'll do the research further needed to understand it.

Years ago, I was told that the force applied on my back while brushing my teeth leaning is about a 2000kg, and putting a hand down on the sink would make this force become 0. I found this very weird but lately I started doing some work with motors and found the force of torque, so this feels a little more possible but still kinda wrong.

So let's get to it. Assuming I lean forward while brushing, my weight would have some force on the pivot point of my back.

Let's assume that pivot point is 95cm above the ground, and the top of my head is 171cm above the ground. This gives us a total of 76cm from the top to the pivot point.

Let's also assume that the weight above the pivot point is 55kg and that it's spread equally throughout the height.

We'll also assume that the leaning angle is 25° from the position where I'm standing straight.

How can I calculate the torque (or whatever units of measurement would be appropriate here) applied on that pivot point?

Bonus: How can I calculate the torque applied when putting a hand down? You are welcome to assume anything here since I don't even know what variables would be needed for such a calculation.

Thanks a lot!

This is a question I've had for several years but never had the knowledge to calculate myself. Please keep in mind I don't have much background in physics (learned some on middle school I guess...), but I'd still love a thorough answer and I'll do the research further needed to understand it.

Years ago, I was told that the force applied on my back while brushing my teeth leaning is about a 2000kg, and putting a hand down on the sink would make this force become 0. I found this very weird but lately I started doing some work with motors and found the force of torque, so this feels a little more possible but still kinda wrong.

So let's get to it. Assuming I lean forward while brushing, my weight would have some force on the pivot point of my back.

Let's assume that pivot point is 95cm above the ground, and the top of my head is 171cm above the ground. This gives us a total of 76cm from the top to the pivot point.

Let's also assume that the weight above the pivot point is 55kg and that it's spread equally throughout the height.

We'll also assume that the leaning angle is 25° from the position where I'm standing straight.

How can I calculate the torque (or whatever units of measurement would be appropriate here) applied on that pivot point?

Bonus: How can I calculate the torque applied when putting a hand down? You are welcome to assume anything here since I don't even know what variables would be needed for such a calculation.

Source Link
Yoda
Yoda
  • 11
  • 1

What is the amount of force applied on my back while I'm brushing teeth leaning forward?

This is a question I've had for several years but never had the knowledge to calculate myself. Please keep in mind I don't have much background in physics (learned some on middle school I guess...), but I'd still love a thorough answer and I'll do the research further needed to understand it.

Years ago, I was told that the force applied on my back while brushing my teeth leaning is about a 2000kg, and putting a hand down on the sink would make this force become 0. I found this very weird but lately I started doing some work with motors and found the force of torque, so this feels a little more possible but still kinda wrong.

So let's get to it. Assuming I lean forward while brushing, my weight would have some force on the pivot point of my back.

Let's assume that pivot point is 95cm above the ground, and the top of my head is 171cm above the ground. This gives us a total of 76cm from the top to the pivot point.

Let's also assume that the weight above the pivot point is 55kg and that it's spread equally throughout the height.

We'll also assume that the leaning angle is 25° from the position where I'm standing straight.

How can I calculate the torque (or whatever units of measurement would be appropriate here) applied on that pivot point?

Bonus: How can I calculate the torque applied when putting a hand down? You are welcome to assume anything here since I don't even know what variables would be needed for such a calculation.

Thanks a lot!