[Guest]

I have two identical uniform plastic blocks, 2x1x1, on a slope of uniform roughness. One is standing up on end. As i increase the slope, which starts to slide first?? Can anyone reconcile this with friction=coefficient of friction*normal reaction force??

(none of my physics or maths teachers could answer this, and i need it for a real life application)

[Guest]

i think the block standing upright has more tendency to topple than sliding thus the second block will slide first

[Guest]

i think the block standing upright has more tendency to topple than sliding thus the second block will slide first

i guess it would be more likely to topple but surely that would start it sliding sooner?

anyway imagine it doesn't

[curr3nt]

I think you are joking...

Excluding toppling... they will slide together.

Friction isn't dependant on surface area.

A source: http://www.physlink.com/education/askexperts/ae140.cfm

[Peekay]

Since the mass of both bodies are the same, the normal force would be the same and so would the force of friction. They would start to slide at the same angle.

Note: The frictional force is independent of surface area of contact.

[Guest]

i think in friction problems we assume there is no forces of attraction b/w the surface and block.... but in practical scenarios it is proved that forces of attraction are present and it depends on surface area..... e.g. it is difficult to separate 2 silver foils which are not joined together but are in contact...

[Guest]

In the case of silver foils or even simple paper its not friction but the static charge that causes difficulty in separation.

[Guest]

In the case of silver foils or even simple paper its not friction but the static charge that causes difficulty in separation.

my physics teacher once told us that the silver foil is very smooth.. and thus more microparticles of 2 foils are in contact and thus forces of attraction are more b/w them.

[mewminator]

i guess it would be more likely to topple but surely that would start it sliding sooner?

anyway imagine it doesn't

static friction > dynamic (kinetic) friction

toppling over means there's kinetic energy

therefore the friction is less which will most likely to get it sliding depending on the roughness

[bonanova]

Classical treatment of friction says it's independent of surface area.

I'm betting your experiment shows otherwise, and that greater surface area gives [slight but measurably] greater friction.

The simple coefficient of friction formula is practical in use, but nonetheless approximate.