Thursday, August 27, 2015

Forces | 9702 Physics Summary Notes

  • 5. Forces | 9702 Physics Summary Notes

· Force: rate of change of momentum

· Finding resultant (nose to tail):
o By accurate scale drawing
o Using trigonometry

· Forces on masses in gravitational fields: a region of space in which a mass experiences an (attractive) force due to the presence of another mass.

· Forces on charge in electric fields: a region of space where a charge experiences an (attractive or repulsive) force due to the presence of another charge.

· Upthrust: an upward force exerted by a fluid on a submerged or floating object
· Origin of Upthrust:
Pressure on Bottom Surface > Pressure on Top Surface
 Force on Bottom Surface > Force on Top Surface
 Resultant force upwards

· Frictional force: force that arises when two surfaces rub
o Always opposes relative or attempted motion
o Always acts along a surface
o Value varies up to a maximum value

· Viscous forces:
o A force that opposes the motion of an object in a fluid;
o Only exists when there is motion.
o Its magnitude increases with the speed of the object

· Centre of gravity: point through which the entire weight of the object may be considered to act

· Couple: a pair of forces which produce rotation only

· To form a couple:
o Equal in magnitude
o Parallel but in opposite directions
o Separated by a distance
· Moment of a Force: product of the force and the perpendicular distance of its line of action to the pivot 

· Torque of a Couple: the product of one of the forces of the couple and the perpendicular distance between the lines of action of the forces.

· Conditions for Equilibrium:
o Resultant force acting on it in any direction equals zero
o Resultant torque about any point is zero.

· Principle of Moments: for a body to be in equilibrium, the sum of all the anticlockwise moments about any point must be equal to the sum of all the clockwise moments about that same point.

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