ODU (part 1) Flashcards
What is a scalar?
A scalar is a quantity that has size (magnitude) only
What is a vector?
A vector is a quanity that has size (magnitude) and direction
Name 6 examples of scalars
Distance
Speed
Energy
Temperatire
Time
Volume
Name 5 vectors
Velocity
Displacement
Weight
Force
Define distance
Distance is a scalar. It is the total length of the path an object has travelled.
Define displacement.
Distance is a vector. It is a measure of how farn an object has moved directly from its start point to its finish point in a straight line.
What happens if an object changes its direction during a journey
its average speed and average velocity for the journey will be different.
Formula for speed
V= d/t
V= speed measured in metres per second (ms^-1)
d = distance measured in metres (m)
t = time measured in seconds (s)
Formula for velocity
V = s/t
V = velocity measured in metres per second (ms^-1)
s = displacement measured in metres (m)
t = time measured in seconds (s)
Define acceleration
acceleration (a) is the change in velocity per unit time
What is acceleration measured in
metres per second per second (ms^-2)
Describe an experiment to measure the acceleration of an object down a slope.
Use a cart with card on it, place it let it roll down a slope and use a light gate connected to a computer to find out its final speed and time taken to pass the light gate. substitue these values into the acceleration formula.
What are the 4 equations of motion
V = u + at
S = ut + 1/2at^2
V^2 = u^2 + 2as
S = 1/2(u+v)t
Where:
S = displacement measured in metres (m)
u = initial velocity measured in metres per second (ms^-1)
v = Final velocity measured in metres per second (ms^-1)
a = acceleration measured in metres per second per second (ms^-2)
t = time measured in seconds (s)
How to find displacement and acceleration in a velocity time graph
Find the area under the graph to find the displacement and gradient of the line to find the acceleration.
What are the conditions for equations of motion to be used
The motion is a straight line
The acceleration is constant
What is the acceleration due to gravity (Vertical motion)
-9.8 ms^-2 (downwards)
The final velocity of an object falling 10m would be (+/-)
negative
Tne initial velocity of an object being thrown upwards 10m would be (+/-)
positive
How do you find acceleration in a speed time graph
gradient of the graph.
How do you find distance travlled in a speed time graph
Area under the graph
How do you find displacement in a velocity time graph
area under the graph
How do you find the velocity in a displacement time graph
gradient
how do you find the acceleration in a velocity time graph
gradient
How do you find change in velocity in an acceleration time graph
area under the graph.
an accelerataion time graph shows…
the gradient of the velocity time graph at all points.
A change in objects motion to the opposite direction means that the velocity/acceleration time graphs will…
“change signs” ie go from postive to negative.
State Newtons first law
An object will remain at rest or traavel at a constant speed in a straight line (constant velocity) unless acted on by an unbalanced force.
State Newtons second law
The acceleration of an object varies directly with the unbalanced force applied (constant mass) and inversely with the mass. (constant unbalanced force)
State Newtons third law
For every action there is an equal but oppositie reaction force.
Relationship for unbalanced force
F = ma
F = Unbalanced force measured in Newton (N)
m = mass measured in kilograms (kg)
a = acceleration measured in metres per second per second (ms^-2)
Relationship for weight
W = mg
W = weight measured in Newtons (N)
m = mass measured in kilograms (kg)
g = gravitational field strength measured in newtons per kilogram (Nkg ^-1)
(9.8 Nkg^-1 on earth, otherwise stated in question or in data booklet)
Relationship for work done
Ew = Fd
Ew = work done measured in Joules (J)
F = force applied measured in Newtons (N0
d = distance measured in metres (m)
What happens to air resistance on a falling objhect
The air resistance increases with speed. Once the air resistance on an object is large enough to balance the downward force of weight the object will fall with a constant speed. this is called the terminal velocity.
What does the reading on a mass scale tell us
reading on scale = reaction force upwards.
If lifts are stationary or moving with a constant velocity…
Reaction force = Weight
If lifts are accelerating upwards or decelerating downwards…
Reaction force = Weight + unbalanced force
If lifts are accelerating downwards or decelerating upwards
Reactilon force = Weight - unbalanced force.
How do you find acceleration of a whole joint system where friction can be ignored
Tensions cancel out. Put unbalanced force and total mass in F=ma to find a.
How do you find the tension of an individual towed object where friction can be ignored.
Use F=ma to find unbalanced force on the object (note that if the link is pulling multiple objects all masses have to be considered)
What must you do when towed objects have friction
the calculated tension (unbalanced force) must be added to the frictional force acting on the object.
How do you calculate a resultant force
create a right angle triangle and use pythagoras to figure out the magnitude and trignometry (sohcahtoa) to find the direction.
How do you resolve vector components
Resolve into two perpendicular components, usually vertical and horizontal.
Trigonometry can be used to find the magnitude of each component.
What direction does friction act in (on a slope)
Friction always acts in the opposite direction to motion on a slope
Formula for parallel weight
W(parallel) = mgsin0
W = weight measured in Newtons (N)
m = mass measured in kilograms (kg)
g = gravitational field strength measured in newtons per kilogram (Nkg^-1)
0 = angle of slope.
Formula for perpendicular weight
W(perpendicular) = mgcos0
W = weight measured in Newtons (N)
m = mass measured in kilograms (kg)
g = gravitational field strength measured in Newtons per kilogram (Nkg^-1)
0 = angle of slope.
How do you find unbalanced force going down a slope
Unbalanced force: mgsin0 - friction
State the law of conservation of energy
Energy cannot be created or destroyed only transferred from one form to another.
Formula for kinetic energy
Ek = 1/2mv^2
Ek = kinetic energy measured in Joules (J)
m = mass measured in kilograms (kg)
v = velocity measured in metres per second (ms^-1)
Formula for gravitational potential energy
Ep = mgh
Ep = gravitational potential energy measured in joules (J)
m = mass measured in kilograms (kg)
g = gravitational field strength measured in newtons per kilogram (Nkg^-1)
h = height measured in metres (m)
Formula for power
P = E/t
P = power measured in Watts (W)
E = energy measured in joules (J)
t = time measured in seconds (s)
Formula for momentum
p =mv
p = momentum measured in kilograms per metres per second (kgms^-1)
m = mass measured in kilograms (kg)
v = velocity measuerd in metres per second (ms^-1)
What are the two types of collision
Elastic collision
Inelastic collision
State the law of conservation of momentum
The total momentum of a system does not change in a collision or explosion in the absence of external forces.
the direction of momentum is always the same as
the direction of velocity.
What happens to momentum and kinetic energy in an inelastic collision
Total momentum is conserved
Kinetic energy decreases
What happens to momentum and kinetic energy in an elastic collision
Total momentum is conserved
Kinetic energy is conserved
Formulae for momentum questions
(m1+m2)u = m1v1+m2v2
(m1+m2)v = m1u1+m2u2
m1u1+m2u2 = m1v1+m2v2
What is impulse
change in momentum
Formula for impulse
Ft = mv - mu
F = (mv-mu)/t
What are the units of impulse
Ns or kgms^-1
How do you find impulse from a graph
Calculate the area under a force time graph (impulse is equal to Ft)
