CP PHYSICS
FORCES NOTES
Four kinds of Forces:
1)
Gravitational force
 force of attraction between two masses
 weakest of the four forces
2)
Electromagnetic force
 force resulting from moving electric charges
 gives materials their strength, ability to bend, squeeze, stretch,
or shatter
3)
Strong nuclear force
 holds particles in nucleus of the atom together
 strongest of the four forces
4)
Weak force (weak nuclear force)
 form of electromagnetic force
 involved in radioactive decay
NOTE:
contact between objects not necessary some forces act over a
distance
Equilibrium Forces:
 concurrent forces are two or more forces acting on the same point at
the same time
 the resultant force equals the concurrent forces added together
 when all external forces acting on an object cancel out, then Fnet =
zero, the object is said to be in a state of equilibrium (object is at rest
or moving at constant speed – 1st Law)
 single force that can put an object in state of equilibrium = equilibrant
force, it is equal in magnitude but opposite in direction to the resultant
force
 ex. resultant = 45 N, east, the equilibrant = 45 N, west
Friction:
 force that opposes motion
 objects must be in direct contact with each other
 acts parallel to surfaces involved
 opposite direction as the motion of the objects
 2 causes: 1) microscopic bumps
2) electromagnetic force (temporary attractions between
contact points)
 2 types:
1) static – opposes the start of motion
2) sliding – force experienced by objects already moving
against each other
CP PHYSICS, FORCES NOTES, page 2
Friction: (cont’d)
 static friction is always greater than sliding friction
 force of friction depends on: 1) nature of the two surfaces
2) smoothness of the surfaces
3) normal force pressing surfaces
together
Normal force = force equal in magnitude to weight by opposite in direction
to weight (points upwards)
Centripetal Force:
 causes object of follow a circular path
 centripetal = “center seeking”
 examples:
1)
moon in orbit around the earth
2)
electrons moving around the nucleus of an atom
3)
the tub in a washing machine
a)
force acts on the clothes not the water
b)
water has inertia and leaves the tub through the holes
c)
water has a straight path
4)
car going through curve experiences friction between the tires
and road which provides the centripetal force
 centrifugal force – NOT real force, due to object’s inertia (wanting to
move in a straight line not a circular path
*rubber stopper on a string swung in a circle – the force stops when
the string breaks and the stopper moves off in a straight line path
according to Newton’s 1st law
*way to simulate gravity on a space station is to rotate it so inertia
provides the sensation of weight