Material + Measurements Flashcards
(35 cards)
What is Density (p) ?
is a measure of the compactness of a substance
- Measured in Kgm^-3
How to calculate Density ?
p = m/v
(Density = mass/volume)
- determines whether object floats or sinks, low density float on high density
What is Hooke’s Law
the force applied is proportional to its extension of a stretched wire in
UP TO LIMIT OF PROPORTIONALITY
How to calculate the Spring constant (k) ?
spring constant = stiffness
F = KΔL
Hooke’s Law in springs ?
can have tensile forces and compressive forces
- K = K1 + K2 (parallel)
- 1/K = 1/K1 + 1/K2 (series)
What is the elastic limit ?
the maximum extension without permanent deformation
- past limit = permanently changed
What is the limit of proportionality ?
the material no longer obey’s Hooke’s law ( not linear graph)
What is elastic deformation ?
the material will return to its original shape once force is removed
- under tension atoms pulled apart but can go small distance without changing position
What is Plastic Stretch ?
the material is permanently stretched once force is removed
What is Tensile Stress ?
the force applied divided by cross sectional area
= F/A
- Measured in Nm^-2
What is Tensile Strain ?
is the change in length divided by original length = ΔL/L
What is Breaking stress ?
at point UTS - ultimate tensile stress
- maximum force = maximum stress
- stress cause atoms to separate completely
How to calculate elastic strain energy in a stretched material ?
E= 1/2FΔL
- area under F/ΔL graph
- derive
1) work-done = force x displacement
2) work-done = 1/2Fx
3) work-done = 1/2kx^2
What is the young modulus (E) ?
is the measure of how stiff a material is
E = stress/strain
E = FL/AΔL
What is the gradient of a stress/strain graph ?
is the young modulus
What is the area under the stress/strain graph ?
is the strain energy per unit volume (1/2 x stress x strain)
- ONLY UP TO THE LIMIT OF PROPORTIONALITY
What is the Yield (Y) point of a material ?
permanent deformation and wire weaken temporarily
What is meant by brittleness ?
material snaps without any noticeable yield
- e.g. glass
- bigger gradient on stress-strain graph
- brittle fracture = little plastic deformation
What is meant by Ductile ?
can be drawn into a wire
- e.g. copper
- lower gradient on stress-strain graph
What are the Prefixes ?
Tera - T - 10^12 Giga - G - 10^9 Mega - M - 10^6 Kilo - K - 10^3 Centri - C - 10^-2 Milli - m - 10^-3 Micro - u - 10^-6 Nano - n - 10^-9 Pico - p - 10^-12 Fermi - f - 10^-15
What is Random error ?
the reading tends to spread out due to results varying in an unpredictable way
How to reduce random error ?
- increase value as large as possible
- increase precision of the equipment e.g. micrometer
- estimate true value
= MEAN ± 1/2 RANGE
What is Systematic error ?
predictable and consistent departures from the true value due to problems with the calibration of your equipment.
- due to environment
- hard to sport error
Examples of Systematic errors ?
1) Parallax error - look at apparatus at wrong angle
2) Zero error - failing to read zero
3) Percentage error - count 20 oscillations instead of 19
