2. the bull I ride is not mechanical [COMPLETE] Flashcards
mechanics
What is mass?
the amount of matter something contains, kg
What is weight?
the force due to gravity pulling two objects together, N
What is g?
The acceleration due to gravity
What is normal contact force?
a force perpendicular to a surface stopping two objects crushing together.
What is tension?
a force which can be due to compression of stretching of a material
it always comes in pairs
What is tension due to stretching?
the materials molecules are pulled apart and an attractive electromagnetic force between the molecules pulls them back together
What is tension due to compression?
the material molecules are pushed together and a net repulsive electromagnetic force tries to push them further apart
What is friction?
a force that acts against motion between two surfaces in contact.
parallel to motion in the opposite direction
What does the size of a frictional force depend on
- type of surface
- how hard the surfaces are pressed together
What is moment?
turning effect on an object. It is the product of the distance perpendicular to the force and the force applied.
What is the moment of a force about a point (Nm)?
force (N) * perpendicular distance from the force (m)
What is “couple”?
two forces that are equal and opposite do not act along the same line meaning there is no resultant force but still a turning effect.
What is the principal of moments?
when an object is in equilibrium the sum of clockwise moments about any point equals the sum of anticlockwise moments about the same point
What is the centre of gravity?
the point at which we can take its entire weight to act, THERE IS NO MOMENT DUE TO WEIGHT
What is the centre of mass?
the point at which we can take the entire mass to be concentrated
What is a stable object?
the centre of mass and line of action lies between the objects base/supports
How do you locate the centre of mass?
hang the shape from a pivot point with a plum line and nail
trace along the plum line
repeat from at least 2 more pivots
where all the lines cross is the CoM
(the CoM must be along the line of action because there are no resultant moments)
What is distance?
how much ground an object has covered during its motion (scalar quantity)
What is displacement?
how far out of place an object is and the overall change in the objects position (vector quantity)
What is speed?
rate of change of distance
What is velocity?
rate of change of displacement
What is acceleration?
rate of change of velocity
What do straight lines on a displacement time graph represent?
constant velocity (if flat the velocity = 0)
How do you find the instantaneous velocity from a displacement time graph?
draw a tangent and find the gradient
How do you find the distance of the journey from a displacement time graph?
sum of slope height (not inc negatives)
How do you find the displacement of the journey from a displacement time graph?
sum of slope heights inc negatives
How do you find the acceleration from a displacement time graph?
find the initial and final velocity at two points by finding the gradient
divide by the time between the two points to get acceleration
What does the gradient of a velocity time graph represent?
acceleration
What does the area under a velocity time graph represent?
distance/displacement depending on negatives
When can suvat equations be used?
when an object moves with constant uniform acceleration
What is free fall?
the only force acting on an object is gravity. Accelerate downwards at the same rate
What is terminal velocity?
the highest attainable velocity of an object as it falls through a fluid. the drag = weight.
terminal velocity can be different speeds i.e. a skydiver will have two different terminal velocities depending on if the parachute is open.
When is an object following projectile motion?
an object follows a parabolic path
How do you approach a projectile question?
resolve the initial velocity into horizontal and vertical components
acceleration only acts on the vertical component and is g.
horizontal distance can be easily calculated using the equation s = vt
What is Netwon’s first law?
an object will remain at rest or travelling at a constant velocity, until it experiences a resultant force
What is Newton’s second law?
the rate of change of momentum of an object is directly proportional to the resultant force acting on it and will act in the same direction as that force
F = (mv-mu)/t or F=ma
What is Newton’s third law?
If object A exerts a force on object B then object B exerts an equal and opposite force back on A
What are the conditions to have a Newton’s third law pair? (5)
- forces must have the same magnitude
- forces act along the same line but in opposite directions
- forces act for/at the same time
- forces act on a different object
- forces are the same type
What is work done?
the energy transferred whenever a force moves an object over a distance. scalar quantity measured in joules.
What is the equation for work done?
force, F (N) * displacement in the direction of the force, s (m)
If the force and displacement are not in the same direction when calculating work done:
resolve the force
W = Fcosx * s
What is energy?
the ability to do work
What does 1 joule represent?
the work done when a force of 1N moves through a distance of 1m in the direction of the force
What is power?
rate of doing work
What is the equation for power?
= work done, w(J) / time takens, t (s)
= force, F (N) * velocity, v (m/s)
What is kinetic energy?
the energy an object has because of its motion
What is the equation for kinetic energy?
1/ 2 * m* v^2
What is potential energy?
the energy stored in an object due to its position, state or shape
e.g. gravitational, chemical, elastic, electrical or nuclear
What is the equation for gravitational energy?
mgh
What is the equation for elastic potential energy?
= 1/2Fx
= 1/2 kx^2
When is constant velocity achieved?
When there is no resultant force and no work is done
What is the principle of conservation of energy?
energy can be transferred from one form to another, bu it cannot be created or destroyed. The total amount of energy always remains the same.
What is efficiency?
the proportion of energy that is usefully transferred is called the efficiency of the machine
What is the equation for efficiency?
useful out/total in
List the suvat equations (4)
v=u +at
s=(u+v)/2 t
s=ut + 1/2a*t^2
v^2=u^2 + 2as
What is a free-body diagram?
a free body diagram whoch shows all the forces that act on an object
How do you prove N1L using N2L?
if resultant force is 0 and acceleration is 0
F=0
a=0
0=m*0
0=0
When does terminal velocity occur?
when the frictional forces acting on an object and the driving forces are equal, so no resultant, no acceleration, so it travels at constant velocity
What is the equation for momentum?
momentum = mass * velocity
What is the unit for momentum?
kg m s^-1
What is the principle of conservation of linear momentum?
momentum is always conserved in any interaction where forces act.
momentum before = momentum after
How do force and momentum link?
force is the rate of change of momentum
F=change in momentum/change in time period
Where does the weight act upon the object?
the centre of gravity
What is the formula for work done (trig)?
W.d. = force * distance * cos θ
What is gravitational potential energy?
the energy that an object has due to its position in a gravitational field
What is power?
the rate of energy transfer
What is an alternative formula for power?
Power = force * velocity
P = W/t
P = (Fd)/t
P = Fv
What must always be true when using the SUVAT equations of motion?
The acceleration must be uniform - if the acceleration is changing, the equations are not valid.
What does the gradient of a distance-time graph represent?
Speed
What does the gradient of a displacement-time graph represent?
Velocity
What does the gradient of a velocity-time graph represent?
Acceleration.
Describe the shape of a velocity-time graph for an object travelling with uniform acceleration.
If acceleration is constant, the gradient of the velocity-time graph will be constant and so it will form a straight line graph.
Describe the shape of a velocity-time graph for an object travelling with non-uniform acceleration.
If acceleration is not constant, the gradient of the velocity-time graph will change and so it will form a curve.
Compare the velocity-time graphs for a uniformly accelerating and a uniformly decelerating object.
● For an accelerating object, the gradient will be positive
● For a decelerating object, the gradient will be negative
Give five examples of scalar quantities.
- Distance
- Speed
- Mass
- Energy
- Temperature
Give five examples of vector quantities.
- Displacement
- Velocity
- Acceleration
- Momentum
- Force
How is a vector quantity represented on a diagram?
● As an arrow
● The direction of the arrow represents the direction of the quantity
● The length of the arrow represents the magnitude of the quantity
