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Dynamometer and Weight

  • Thread starter Lunny
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Homework Statement


I am trying to help my lil bro (12 yo) with some physics. I've never been good in physics and now it's been more then 10 years that i've been to elementary school.

I've helped him with some stuff but there's this one question that i don't understand and there's very little material on it in his book. It's about a dynamometer and weight. It asks if we put an object that weighs 0.5kg in the dynamometer what will the weight be?



Homework Equations





The Attempt at a Solution


Logicaly i assume that it would be 0.5kg but i am not sure. Perhaps the result must be in N(ewton)?

We haven't tried the F = 0.5kg * 10 N/kg, formula. As i am not sure if it's right in this case with dynamometer.

Should the result be in KG or N, or something else?

He has a test in a couple of days and it would really help him/us.

Please advice.
 

Answers and Replies

  • #2
PhanthomJay
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In Physics, the weight force is given in Newtons. The mass is 0.5 kg, the weight is mg = 5 N, as you have noted (using g= 10 m/s^2, it is actually 9.8 m/s^2). So yes, 1 kg weighs about 10 N , on Planet earth, and the dyno reads that value.

I should note, however, that being from the States, I've never been to a country that uses Metric units, but i understand from others that if you place a kilogram of bananas on a scale in a grocery store, the scale will read 1 kg, not 10 N. I don't think the ordinary layman knows what a Newton is, but I'm not sure. Maybe someone from any country besides the USA and Myanmar (formerly Burma) can help out.:wink:
 
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As the question is what weight will the dynamometer show, the answer will be expressed in Newtons.
My opinion here is that there's no need to fuss over the dynamometer whilst searching for the solution of the problem; the problem itself could have been stated in a simpler manner, e. g. "If the mass of an object is 0.5kg, what is it's weight?"

You might want to explain the difference between mass and weight to your brother.
Btw, the value for "g" isn't the same everywhere on earth, but with 9.8N/kg or 9.81N/kg, you'll be fine. Don't use 10N/kg, except if your bro's teacher says it's OK.

P.S.
Slightly offtopic. I'm not quite sure that I understand the relevance of grocery store scales for this question, but, no, the scales in e. g. Europe aren't in Newtons - they're in kilograms. :)
(I'm questioning the relevance as, afaik, dynamometers always show results measured in weight units, not mass units.)
 

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