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Applying moments to gain mechanical advantage
Meet the spec - What you need to know!
Meet the spec - What you need to know!
As you can see, it's not to bad. You just need to be able to calculate moments and apply them to lever and gear systems.
Levers
Levers
Wheelbarrow
Claw Hammer
Scissors
These are all examples of levers. The wheelbarrow has a pivot around its wheel, the hammer pivots around its head and the scissors pivot in the middle. We use these tools to make work easier. We are applying moments to gain a mechanical advantage and we didnt even realise it.
These are all examples of levers. The wheelbarrow has a pivot around its wheel, the hammer pivots around its head and the scissors pivot in the middle. We use these tools to make work easier. We are applying moments to gain a mechanical advantage and we didnt even realise it.
task 1 - watch the intro
task 1 - watch the intro
Watch the video to 3:53
Answer the questions on the companion sheet.
Worked example
Worked example
At what is the minimum distance a 400N force could lift a 200kg boulder, if the boulder was 0.4m away from the pivot? (assuming gravity of 9.8N/kg)
Using W=mg we can find the weight of the boulder - 1960N
Then we work out the moment of the boulder using M=Fd - 784Nm
Now we know that we need to provide a moment at the opposite side of the pivot ≥ 784Nm to lift the boulder.
We know the target moment is 784Nm and the maximum force we can apply is 400N .
Using M=fd rearranged for 'd' (d=M÷F), we can work out 784÷400 = 1.96m
The minimum distance we could lift the boulder at is 1.96m
If we move further away from the pivot, we can use less force.
"Give me a lever long enough and a fulcrum on which to place it, and I shall move the world."
"Give me a lever long enough and a fulcrum on which to place it, and I shall move the world."
(Archimedes 287-212 BCE)
Task 2 - Practise
Task 2 - Practise
Work your way through the practise question ,step-by-step.
Look at the lever scenario and used youe existing knowledge to answer the question.
Task 3 - Back to gears!
Task 3 - Back to gears!
Watch the video and answer the questions
Task 4 - its all about radius
Task 4 - its all about radius
We used to work out the magnification of the forces by the ratio of the numbers of the teeth on the gears. (Which still works btw)
If you look at the 2 gears in the picture opposite you can see that from the pivot at the center of the gear, there are different distances to the edge of the gear where the force is applied. This means that they have 2 different moments, a gear is just another type of lever if you think about it....
Work out the moments
Work out the moments
Finish the companion sheet
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