Q: "On my physics homework one of the questions said ' What would the weight be of a hammer weighing 1.32 kg on the moon?' It says that Gravity on the moon is approximately 1.67 newtons/kg. Please help! thank you :)"
A: "Since the weight is 1.67 newtons for each kg, then multiply this by the number of kg to get the weight in N."
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Posted by JT on 22 Oct 2009.
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Now, I'm no physicist but it seems to me that if this answer was correct the hammer would actually weigh more on the moon. Which seems rather unlikely, as we know lunar gravity is around 16.5% that of Earth.
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Posted by JT on 22 Oct 2009.
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Looks OK to me. Little 'g' on Earth is about 9.81 N/kg. 1.67 is ~17% of 9.81 which is consistent with your 16.5%.
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Posted by Wrongfellow on 22 Oct 2009.
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I used Earth g of about that figure, only with a few nore decimal places and worked out that you'd need to divide earth weight by 5.8744 (or something, can't remember now) - it was slighly under the sixth or 16.5% theytell you at school, but close enough to assume I was on the right track. By my reckoning, on the Moon the hammer would weigh about 0.22 kg - whereas using the formula above, it'd be 1.67kg.
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Posted by JT on 22 Oct 2009.
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Er...a few MORE decimal places. Still not used to this keyboard!
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Posted by JT on 22 Oct 2009.
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Ah bollocks. Now I've thought about it using my head instead of trying to use a calculator, I'm not too sure how I managed to come up with 1.67kg (and had to come back and switch the computer back on). Oh well. (-) it is, then :-)
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Posted by a mysterious, unknown entity on 22 Oct 2009.
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On Earth we often use kilograms for both mass and weight, but when you're dealing with variable gravity it's important not to confuse them with each other. It's more precise to measure mass in kg and weight (acceleration due to gravity) in N.
Also we often use the term "weighs" ambiguously. The mass of the hammer is given as 1.32 kg, and in this sense it weighs 1.32 kg on both Earth and the Moon.
On Earth 1.32 kg * 9.81 N/kg =~ 12.95N
On the Moon 1.32 kg * 1.67 N/kg is ~2.2 N.
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Posted by Wrongfellow on 22 Oct 2009.
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I remembered the kg as mass stuff from school (and therefore the mass remaining the same in either situation). It was while trying to convert newtons into kg that things went wrong - I committed the cardinal sin of accepting what the calculator was telling me even though my instincts were trying to say "Erm..!"
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Posted by JT on 23 Oct 2009.
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Science is so screwed up.
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Posted by Socky on 23 Oct 2009.
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