# Mechanics and Materials

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Energy/Distance
Force
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Why would mass calculations be incorrect?
-mass/weight changes -air resistance changes -gravity changes -overall net force change
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Limit of Proportionality
When the force/stress proportional to extension/strain and so it obeys Hooke's Law
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Tensile Strength
The maximum stress before fracturing
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Yield Point
where plastic deformation begins and so strain increases more than stress
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What happens if you decrease the volume of a submerged object?
The upsthrust wiill also decrease
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How do you keep a submerged object and a constant depth if the volume is decreased?
You need to decrease the mass to keep the density the same as the surrounding water
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What would a better reaction time benefit within an experiment?
Accuracy
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Area under a force-area graph
Energy stored in the material
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Energy loss (air resistance and friction)
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Projectile
Any object upon which the only force is gravity
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Projectile- horizontal motion
no downwards force or acceleration, constant velocity
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Projectile- vertical motion
the force of gravity, acceleration down of 9.81m/s, changing velocity
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When will velocity go below the x axis on a velocity-time graph?
When the object changes direction because velocity is a vector
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Energy in a Pendulum
It is conserved
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Mass units
Kilograms
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Increasing Acceleration
KE and Speed also increase
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Horizontal Distance Equation
speed=distance/time
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Vertical Distance Equation
s=ut+1/2at^2
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Vertical Velocity Equation
Vv=Vsintheta
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Horizontal Velocity Equation
Vh=Vcostheta
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Time to reach max height equation
t=(v-u)/a
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What is rubber not?
Stiff
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The energy lost to surroundings
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When a rubber band is stretched
Less energy is given out than stored as internal energy
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Work done
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A weaker material and Compressive Strain
The strain experienced would be larger and so the volume/upthrust will decrease, thus breaking or sinking
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Stopping objects with larger masses
The KE of the object will be larger and so a larger force and more work done is required
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Falling Elastic Objects
-GPE is converted into KE -KE is converted into ElPE when the object/rope compresses/stretches -ElPE is then converted back into KE
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Laminar
No abrupt changes in direction or speed of flow
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Turbulent
Abrupt changes in direction and speed of flow
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Decreasing the area over which there is turbulent flow
-less resistive force -less KE is dissipated -less work done against air resistance -less decceleration -further range
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Newtons 1st Law of Motion
If there are no external forces, here will be no resultant force and so the object will have a constant velocity
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Similarities between 3rd Law Forces
-equal magnitude -equal line of action -equal time of action -same type
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Differences between 3rd Law Forces
-opposite direction -act on different bodies
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The earth and object 3rd law forces
The earth exerts an upwards force on the object which is equal to the mass and gravitational force of the object
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Explaining Experiments
-apparatus -measured quantities -method of measuring -results and graphs -how results are calculated -repeats and precautions
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What happens if you have a longer length/rope on a vector triangle?
This reduces the size of theta and so a smaller force is required because costheta will be smaller
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What is used to display viscosity values on a graph?
-power of 10 scale -log scale
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Molecular Structure of Elastic Metals
-bonds stretch -bonds don't break -atoms move apart then return
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Molecular Structure of Plastic Metals
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How would a tough material appear on a graph?
-plastic behaviour -large area under linear part
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Crumple Zones
-increase displacement -decrease acceleration -reduce impact force
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Why does acceleration decrease in free fall?
-net force decrease -air resistance increase -the faster he goes the more the acceleration decreases
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What does Stoke's Law Assume?
that there is laminar flow
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Viscous Drag
force which opposes motion through a fluid which has a viscosity
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The Cause of Upthrust
the object displacing the water around it
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Why is terminal velocity represented with F=W-U
-because there is no net force on the object -W=F+U
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What properties does a straight force extension graph show?
elastic and stiff
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Hard
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Tough
large force required to produce a small deformation and deform plastically before breaking
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Forces on an inclined surface
R=0
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Why isn't 100% of energy being transferred in a wind turbine?
because the wind is always moving and cannot all be captured
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mg=
6 pi r n v
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Higher viscosity and speed
slower
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How are wind turbines doing work?
-wind exerts force on blades -blades move through a distance in the direction of the force -
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Work Done?
-what is the force -object moves through a distance in the direction of motion
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GPE=KE
mgh=1/2mv^2
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Resolving Vectors when there are two tension lines
Tsin x 2 = weight/2
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When you can't assume Air Resistance or Friction
-a physical cause eg. distance/movement -energy causes eg. not in the object
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Bungee Free Fall
-free fall when bungee is slack -KE increase as GPE transformed -work done against friction forces -KE converted to EPE when it stretched beyond equalibrium point -at lowest point all KE has been converted into EPE
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## Other cards in this set

### Card 2

#### Front

-mass/weight changes -air resistance changes -gravity changes -overall net force change

#### Back

Why would mass calculations be incorrect?

### Card 3

#### Front

When the force/stress proportional to extension/strain and so it obeys Hooke's Law

### Card 4

#### Front

The maximum stress before fracturing

### Card 5

#### Front

where plastic deformation begins and so strain increases more than stress