Balanced Forces
Vectors
& Scalars
Distance & Displacement
Travel may be longer than direct distance
Displacement - distance in certain direction
Vector quantity
Velocity, Displacement, Force, Momentum, Acceleration
Size (magnitude) and direction needed
Scalar quantity
Mass, Speed, Time, Distance, Energy, Work, Temp.
Magnitude only needed
Vector representation
Represented by an arrow; Length for magnitude, direction
Scale diagram
>1 force acts on object; need a scale
Shows direction, magnitude
Forces
between objects
Definition
Push/pull on an object from another
Contact forces - friction, drag, tension; objects touch
Non-contact - Magnetic, electrostatic, gravity
⭐ Newton's third law
Boxer punches bag w/ 100N; experiences 100N reaction
Gravity/weight - object pulls back on earth w/ same force
Every action has an equal and opposite reaction
Mud
Pull of rope = pull of car
Mud on wheels = wheels on mud
Tractor on mud != Car on mud
Friction
Car's driving force(/engine force) = movement
Road on tyre (forward) = tyre on road (reverse)
Friction acts w/ road-wheel contact causing engine force
Resultant forces
Definition
Single force w/ the same effect as all forces in action
If = 0; then the forces acting are balanced
Newton's First Law
Zero resultant force = resting object or ⭐
Zero resultant force = object w/ no speed or direction change
Pushing at constant speed - equal force to friction - zero
Object will rest/have constant velocity until a force
is acted upon said object
Newton's Second Law
Resultant force != zero; ((F = ma)) ⭐
Resultant force = two force difference
Resultant force direction = larger force
Force on an object w/ fixed mass means
proportional acceleration in the same direction
Free-body force diagram
>1 force on object; only forces on object shown
Each forces shown as a vector
Moments
Levers
Weight of object lifted - load
Turning point - pivot/fulcrum
Force to lift is fraction of load's weight
Force multiplier - effort moves bigger load
Line of action - line force act on
Moment calculation
Moment(Nm) = force(N) by perpendicular distance(m)
M = Fd
Levels
& gears
Force multipliers
Levers incr. force magnitude; force acts further from pivot
Bottle openers, can openers etc.
Gears
Force multipliers - incr. engine force
Gear wheels exert equal/opposite forces in contact
Force acts on a tangent
Low gear
Small engine shaft; Large wheel shaft
Wheel shaft turns slower than engine
Higher turning effect
High gear
Large engine shaft; small wheel shaft
Wheel(/output) shaft turns faster
Low turning effect observed
Centre
of mass
Definition
Can be thought of single point of object's weight
Useful to designing, engineering
Centre of mass is what could be thought of as the concentrated point of an object's weight
Suspended equilibrium
Objects eventually rest if suspended w/ CoM under suspense
Equilibrium - weight exerts no turning force; freely-suspended
Symmetrical object
CoM is along symmetry line/where lines meet
Moments
& equilibrium
Principle of moments
Sum of A.clock moments = sum of clock moments
W1 x d1 = W2 x d2
Parallelogram
of forces
Method
Two tension forces (T1, T2) pull diagonally
Vectors are adjacent parallelogram sides
Diagonal of shape = resultant force (from T1, T2)
Investigation
Pulleys - string tension = weights
W1,W2 pull on W3; middle of strings at rest
Vectors of weights at different angle
Magnitude of force 1 & 2 equal/opposite to 3
Force resolution
Resolving forces
Object on a slope w/ a rectangle; weight = diagonal
Rectangle has perpendicular, parallel side to the slope
Perpendicular side - force on slope
Parallel side - force down the slope
One force vector - two force components
Equilibrium
Resultant = zero, no turning effect
Parallel lines of action have equal force sums
Non-parallel lines resolve onto perpendicular lines