Forces and forcemeters
This Topic is About...
- I will measure forces using a forcemeter.
- I will measure using standard units.
- I will compare standard and non-standard units.
- I will make a bar chart of results.
- I will learn how the science of forces was different in the past.
You’re going to be a science explorer!
Key Words
- forcemeter
- gravity
- newton
- weight
Tap to Learn the Meanings!
- forcemeter: A tool used to measure the size of a force.
- gravity: The force that pulls objects toward the centre of the Earth.
- newton: The unit used to measure force.
- weight: The force of gravity acting on an object.
Great job! You’re learning important physics vocabulary.
Scientists who changed the science of forces
Our understanding of forces was different in the past. Here are three scientists who changed the science of forces.
John Philoponus, lived in Egypt, 490–580
Philoponus wrote that objects move because making them move gives them a force.
Ibn Sina, lived in Iran, 980–1037
Ibn Sina worked out that forces can make objects move.
Isaac Newton, lived in Great Britain, 1643–1727
Newton found out that forces can make objects speed up, slow down or change direction.
Scientists now know lots about forces.
- Forces can make some objects change shape.
- They can make objects speed up, slow down or change direction.
- Mae Jemison was a scientist who investigated forces in space.
Gravity is the force that pulls objects towards the Earth. Gravity makes objects have weight. Weight is another force you can measure.
Let’s Investigate!
Make a simple forcemeter
You will need
- a rubber band
- two paper clips
- a piece of cardboard
- glue
- a piece of lined paper
A forcemeter is a tool we use to measure the strength of a force. Zara has made a simple forcemeter. You can make one too.
Method
- Make a forcemeter like the one shown.
- Mark the end of the rubber band and label this point as zero.
- Number each line below the zero mark.
- Use your forcemeter to measure some forces.
You can measure the force needed to pull objects. For example, a force of 7 lines is needed to make a book move.
These scissors have a weight of 8 lines. Try measuring different forces and make a table of your results.
How am I doing?
Talk to your classmates about the forces you measured.
Did everyone get the same readings?
Is your forcemeter easy to use?
Could you make it more accurate?
Show answers
Key ideas
- The rubber band stretches more when the force is larger.
- The numbered scale helps you compare forces accurately.
- The “zero” mark is important so all measurements start from the same point.
Examples
If the book needs 7 lines of pull, that means your rubber band stretched down to the number 7. If the scissors hang at line 8, their weight is 8 lines.
You may find that heavier or harder-to-pull objects stretch the band more. If two objects stretch the band to the same number, they need the same amount of force.
Standard units and forcemeters
Standard units are useful for measuring.
Metres (m) and centimetres (cm) are standard units of length.
Minutes (min) and seconds (s) are standard units of time.
Standard units are useful because everyone in the world who uses them can compare their measurements.
The standard unit of force is the newton (N). This unit is named after the scientist Isaac Newton. This forcemeter can measure in newtons.
FUN QUESTIONS
1. Name a force you can measure.
Show answer
2. What is the standard unit of force?
Show answer
3. Why are standard units better than non-standard units?
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Let’s Investigate!
Make a better forcemeter
You will need
- your simple forcemeter
- some plain paper
- some glue
- some 100 g masses
The simple forcemeter uses lines as a unit of force. This is a non-standard unit. You can make a better forcemeter by making it measure in newtons (N), the standard unit of force.
On Earth, a 100 g mass has a weight of 1 newton. Zara uses this fact to improve her forcemeter.
Method
- Add a new piece of paper to your forcemeter and mark the zero line.
- Hang a 100 g mass on the forcemeter and mark the 1 N line.
- Add another 100 g mass and mark the 2 N line.
- Mark halfway between each newton mark so you can measure 0.5 N accurately.
- Use your improved forcemeter to measure some forces.
- Make a bar chart to show your results.
After measuring, compare your readings with a friend’s. If your results are different, you should both measure again carefully to decide which measurement is correct.
How am I doing?
Does your scale show clear 1 N and 2 N markings?
Can you measure half newtons accurately?
Are your measurements repeatable?
Does your bar chart clearly show which forces are larger or smaller?
Show answers
Key ideas
- 100 g corresponds to 1 N of weight.
- Each extra 100 g adds another 1 N.
- Marking halfway between the lines lets you measure 0.5 N.
- Using newtons makes your forcemeter a standard, accurate measuring tool.
Example results
If a book pulls the rubber band down to the 1.5 N mark, the force needed is 1.5 N. If a toy car pulls to the 0.5 N mark, its force is 0.5 N.
When you and a friend disagree, measure again and check that the top of the rubber band is exactly level with the scale.