La Force Flashcards
What is Hooke’s Law?
F=kx
where k is force constant, x is extension (or compression) of spring
What is force?
- vector qnty
- SI Unit: Newton (N)
- interact n btw objects, ALWAYS come in pairs
What is full name of a force?
The (type of force) by (object 1) on (object 2), (direction)
Define centre of gravity
of a body is pt where all weight of body may be considered to act
Define centre of mass
of a body is pt where all mass of body seems to be concentrated
What does weighing scale really measure?
Normal contact force
Friction always act in what direction to surface?
parallel
Tensional force always points where?
away fr object, along length of string
How does force constant add up in these combination of springs:
- two in series?
- two in parallel?
- two in parallel each of two sides of body?
- two in series
1/k eff = 1/k1 + 1/k2 - two in parallel
k eff = k1 + k2 - two in parallel each of two sides of body
k eff = k1 + k2 + k3 + k4
(basically opposite behaviour to resistors in parallel and series)
What are the formulae for pressure? Unit?
Unit: Pa (or N m^-2)
Normal: P=F/A
Liquid: P=ρgh
How to derive P=ρgh?
Step 1. Consider point at depth h below liquid’s surface in container
Step 2: Pa can be determined by finding weight of vertical column of liquid acting above area A at that depth
Step 3:
Weight W of column of liquid is:
W=mg=ρVg=ρAhg
Step 4: Since pressure P=F/A,
P = ρAhg/A = ρgh
Absolute pressure at any pt of column of fluid is given by what eqn?
pressure P = (atmos Pa at fluid open surface) +/- ρgh
Define upthrust and give eqn
When object is partially or fully submerged in fluid, it experience upward force known as upthrust. Upthrust results fr diff in hydrostatic Pa btw bottom & top surfaces of object
Upthrust U = Vρg
where ρ & V is density & volume of displaced FLUID
State Archimedes’ Principle
Upthrust acting on object submerged in fluid is equal in magnitude, opp in direct n to weight of fluid displaced by object
State principle of floatation
When object floats in eqm, upthrust acting on object = object’s weight
Define moment of a force. Give eqn
moment of force abt pivot is product of force & perpendicular distance of line of action of force fr pivot
Moment of force abt pivot = F x dsinθ
where θ is acute angle btw direction of force and line d
Define couple. What is the torque of a couple?
- consists of 2 forces, equal in magnitude, opp in direct n & whose lines of action do not coincide
- torque of couple is pdt of one of forces & perpendicular distance between lines of action of forces
What is interesting abt torque of couple?
No matter where pivot is taken (along perpendicular distance btw lines of action of 2 forces), moment is constant
State Principle of Moments
For object to b in rotational eqm, sum of clockwise moments abt any axis must equal sum of anti-clockwise moments abt same axis
What are 2 conditions needed for object at eqm?
- resultant force in any direct n must be zero
- resultant torque abt any axis must be zero
What are other types of forces?
- Lift
- Thrust
- Electric, magnetic, gravitational force
- Stability
