MODULE 3: FORCES AND MOTION Flashcards
stopping distance
THINKING + BRAKING distance
Center of mass
Point where external forces produce a straight line of motion with no rotation
Center of gravity
Point where entire weight of object appears to act
Experiment to find center of gravity
EQUIP: stand, paper, plumb line
EXPERIMENT: suspend paper freely using stand,
Use plumb line to draw a straight vertical line on the object
Rotate the object and do this again
Intersection = center of gravity
What is drag?
Resistive forces when a object moves through a fluid
What is a fluid?
Liquid or gas
What is drag proportional to
Velocity squared
What is terminal velocity
When drag is equal to weight, so Fres = 0.
What is the moment of a force?
Product of force applied and the perpendicular distance of the line of action from the pivot .
Moment equation
Moment = fx so newton meters
What is the principle of moments
Sum of anti-clockwise moments is equal to the sum of clockwise moments about the same point OR axis
Conditions for equilibrium
Fres is zero
Resultant Moment is zero
What is a couple
Two forces equal in magnitude but opposite in direction
What is the torque of a couple
Product of one of the forces (they are the same) and the perpendicular separation between them
How is torque and moment related
Torque is the same as total moment of the two forces about the midpoint between the forces
Density equation
ρ=mass / volume
How to measure density
Measure mass using weighing scale
Measure volume, for regular measure using callipers each edge. For irregular solids find displaced volume using displacement can
What is pressure
Normal force exerted on a surface. Pressure is force over cross sectional area
What is Archimedes principle
The upthrust exerted on a body immersed in a fluid (partially or fully) is equal to the weight of the fluid that the body displaces
What is pressure proportional to and how in a cylinder column
p = f/a
p = mg/a
mass = pressure x volume
p = (ρV)g/a
height = volume / cross section area (v/a)
p = hρg
g and ρ are constant in a cylinder column, p is proportional to the height of the column
What is work done and equation
W = Fx cos theta
Work done is the energy transfer from one to kinetic. One joule is the energy which one joule has moved an object one meter
Formula for GPE and KE
Ek = 1/2 mv^2 Ep = mgh
What is power
Rate of work done, rate of energy transfer
Power equation
P=W/t
How does power relate to force
P = force x velocity
P=Fv
Efficiency equation and what it is
Efficiency = useful energy / total energy
It is a ratio between useful and total energy input or output
Between 0 and 1
Hooke law
The extension of a spring is directly proportional to the force applied
Properties of plastic
Removal of force will not make object return to its original length
Elastic properties
Removal of force makes it go back to its original shape
Elastic potential equation
Ee = half Fx
Elastic potential energy is proportional to what
extension squared
F=is
E=1/2 Fx
so E = 1/2 k x^2
Brittle properties
No deformation before break, they don’t bend they just snap
Ductile properties
Can be stretched and bent and thinned without breaking
What is tensile stress
Same as pressure, force per unit cross sectional area
What is tensile strain
Ratio of extension to the original length.symbol epsilon
What is Young’s modulus
Ratio of tensile stress against strain E = stress / strain
What happens at the elastic limit for brittle vs rubber?
Brittle it snaps
Rubber has no limit
How can the spring equation be put used with the Young’s modulus
E = stress/strain
= (F/A)/(x/L) = Fl/Ax.
E = Fl/Ax, F = EAX/L
F = (EA/L)x, spring constant in F=kx is EA/L
first law of motion
An object will remain at rest or continue to move with a constant velocity until a net resultant force acts upon it
Third law of motion
Who two objects interact an equal and opposite force is always exerted, and a they are the same typr
What is momentum
Product of mass and VELOCITY
What is conservation of momentum
Closed system, total initial momentum is equal to the final momentum
What is an elastic collision
Total KINETIC energy is equal after and before ( no transfer to other stores)
Newton second law of motion
Net resultant force is directly proportional to the rate of change of momentum and is in the same direction
What is the force equation in terms of linear momentum and what is the requirement
for a constant mass object
F = Δp/Δt, = (mv-mu)/Δt = m((v-u)/t) = ma, F = ma
What is the impulse of a force
The product of force and time, and in terms of Newton’s laws it’s the change in momentum (so just momentum units)
What’s the area under force t graph
Force x time = impulse (Δp)
Impulse equation
I = change in momentum
Final velocity and average velocity formula
FINAL = 2 * AV
