Mechanics and materials Flashcards
What shape do objects at equilibrium form in a scalar diagram?
Closed tip too tail
FORM DIAGRAMS TOO SOLVE FOR FORCES
What are the SUVAT equations?
v= u + at
s = ut + 1/2 at^2
v^2 = u^2 + 2as
s = (u+v) / 2 *t
When can you use SUVAT?
Constant acceleration
How do you solve variable acceleration problems?
Energy changes
How long does an object in a vacuum with a higher mass take compared to another of a lower mass and volume?
Where there is no air resistance, all objects in freefall will reach the ground at the same time
Define a moment
The force multiplied by the perpendicular distance too the line of action of that force from the pivot that creates a turning effect
When is a beam on a pivot at its toppling point?
The NCF is 0N
What is a couple?
A pair of forces on the same object equal in magnitude and opposite in direction that don’t act in the same line separated my a distance x
What is the moment of a couple?
F.x
(F is the magnitude of one of the identical forces)
What is the centre of mass?
Where an objects weight is considered to act from
When does an object topple?
The objects COM is above or past the objects pivot point
NOT IN SPEC: What is the topple equation?
tan (toppling angle) = distance between COM and pivot / height of COM above ground
So, lower and wider is more stable as the same mass must be rotated around aa larger angle for it too topple requiring a larger moment.
What are newtons laws of motion?
N1: An object in motion stays in motion unless a force acts upon it (inertia)
N2: Acceleration of a body is directly proportional too the force that acts upon it (constant mass)
N3: If A exerts a force on B, B will exert an equal and opposite force on A of the same type.
What happens to the reading on a scale as a lift accelerates upwards?
The resultant force is upwards so the NCF>Weight. A Scale reads the NCF which is a constant but larger that the real weight of the person.
Explain how an object reaches terminal velocity
Air resistance increases with velocity until the air resistance = weight force
A maximum value of velocity is reached
How are air pressure and air resistance linked?
Increase air pressure, increase fluid density and increase in air resistance acting on any body
What is work done in moving an object?
The energy transfer when a 1N force acts on an object over 1m (in the same direction)
What is power?
The rate of energy transfer
What is gravitational potential energy?
The work done against gravity in lifting a mass (m) by a height (h)
What is the equation for conservation of linear momentum when two objects that collide are travelling in the same directions?
-m1(v1-u1) = m2(v2-u2)
Provided no external forces act upon it
What is the equation for conservation of linear momentum when two objects that collide are head on?
m1(v1-u1) = m2(v2-u2)
Provided no external forces act upon it
How do you solve an elastic collision for multiple unknowns?
Equation in terms of energy and an equation in terms of momentum and solve simultaneously
What is Hooke’s law?
Force on a spring is directly proportion too its extension until its limit of proportionality
How do springs attached too a load in parallel act?
Share the load equally when they have equal spring constants otherwise share the load by proportion
How do springs attached too a load in series act?
They each carry the full load and add thee spring constants onto each other when equal
What is the elastic limit?
The maximum stress a material can experience before it no loner returns too its original shape (begins plastic deformation)
When is the limit of proportionality of a stress strain graph?
End of the linear region (stops following Hooke’s law)
Describe a brittle material graph
Large elastic region, small plastic (non linear)
Describe a ductile material graph
Large plastic region, small elastic (linear)
Describe a strong material graph
High UTS
Describe a stiff material graph
High young’s modulus / gradient
What is necking?
Cross sectional area of a material decreases at the weakest point after UTS and so stress peaks again.
Describe a tough material graph
Absorbs a lot of energy before breaking so a large area under the graph
What is the area under a stress strain graph?
Elastic potential energy per unit volume
What is hysteresis and what does it look like (Force extension graph)?
When elastic materials stretch their chains untangle and fold back down in a different order.
Loading curve is different too the unloading curve.
Compare the area under a loading curve versus unloading
Area unloading < loading as energy is usually lost too heat
What is the yield point?
Where the atomic structure rearranges, a higher yield point means that a material is tougher as it can absorb more energy.
