1. Sofia and Priya investigate friction. Here is the equipment they use.
masses
forcemeter
wooden block
pull
table
material
They put the wooden block with a force meter.
They repeat the investigation using different materials
What two measurements should they make?
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in physics zero. in muscle fatigue could be high

the area between the graph and the t axis

force required to detach it is given by

charges are taken to be fundamental charge

now we have

so above is the minimum distance at which it will detach

3. dark matter

empty space could also be a simple vacuum