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Physics Question: What Happens to Force on the Block When It’s Tilted?

5 min readMay 15, 2025
Photo: Rhett Allain. A block on a tilted incline and one on a flat surface.

Here’s a great physics question for you. A block with mass of 1 kilogram sits on a horizontal table at rest such that the table pushes up on the block with a force of 9.8 Newtons. Nothing crazy there. Next, I tilt the table so that it is 30 degrees above the horizontal but the block stays at rest (it doesn’t slide). What is the new force the table exerts on the block?

Here’s a small hint: I got this question wrong.

Do you have an answer? If your answer is 8.49 Newtons, that’s not correct. Oh, I know what you did. You probably have a force diagram that looks like this.

If we take the y-axis to be perpendicular to the plain then Newton’s second law gives the following two equations (remember the block is at rest so the acceleration is zero).

So, clearly N = mg*cosθ = 8.49 Newtons. Right? NOPE. There’s a small trick. The question asked for the force that the table exerts on the box, not the normal force. Since the box…

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Rhett Allain
Rhett Allain

Written by Rhett Allain

Physics faculty, science blogger of all things geek. Technical Consultant for CBS MacGyver and MythBusters. WIRED blogger.

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