Our dynamic universe Flashcards
sign convention
accelerating left -
accelerating right +
accelerating up +
accelerating down -
(like multiplying eg decelerating left= +
What do we use if something is decelerating due to gravity?
-9.8ms-2
motion time graphs for constant velocity, uniform acceleration and uniform deceleration
show s,v and a
CONSTANT VELOCITY
s/
v—
a__ (@0)
UNIFORM ACCELERATION
s-curve up getting steeper
v/
a—
UNIFORM DECELERATION
s-curve up getting less steep
v\
a— (negative)
What does the gradient of a velocity time graph give?
the value of the constant acceleration
What is happening when a velocity time graph crosses the x-axis?
a change in direction
draw a bouncing ball graph
jotter
For the light gate acceleration experiment, what is needed? (apparatus and measurements)
-QED/computer timer
-tow light gates
-trolley with mask
-stop clock
-initial speed
-final speed
-time
component of forces for F, Fvertical and Fhorizontal
F is acting at an angle x
horizontal component=Fcosx
vertical component=Fsinx
solving systems of masses problems
1-free body diagram (label all forces)
2-find unbalanced for (using total mass)
3-find acceleration (using F=ma)
4-split system into individual bits (label only forces acting on the bit you’re interested in(to find unknown tension or friction))
What is the component of weight parallel to the slope?
mgsinx
What is the component of weight perpendicular to the slope?
mgcosx
lift problems
direction of unbalanced force, F, for
1-constant speed or stationary
2-accelerating up
3-decelerating up
4-accelerating down
5-decelerating down
6-freefall
1-no unbalanced force R=W
2-upwards R-W
3-downwards W-R
4-downwards W-R
5-upwards R-W
6-downwards W only
What is momentum
The momentum of an object is defined as its mass multiplied by its velocity
p=mv
kg ms-1
Momentum experiment measurements
-velocity of trolley A through light gate 1
-velocity of trollies A and B through light gate 2
-mass of trolley A
-mass of trolley B
-mass of trolley A+B
-calculate the total momentum’s of both trolleys before and after the collision
What is the law of conservation of momentum? +equation
‘In the absence of external forces, the total momentum before a collision equals the total momentum after the collision
mAuA + mBuB = mAvA + mBvB
Is sign convention needed for momentum questions and collision questions
momentum-YES
collision-NO (as Ek is a scalar quantity)
Is total energy always conserved in any interaction?
Yes, but for the questions we must focus on kinetic energy when describing elastic and inelastic collisions
What is an elastic collision?
The total kinetic energy of both objects is equal before and after the collision (kinetic energy is conserved)
momentum is also conserved
What is an inelastic collision?
The total kinetic energy of both objects after the collision is less than it was before the collision (kinetic energy is not conserved)
momentum is conserved
What happens to momentum and kinetic energy after an explosion?
momentum is conserved
kinetic energy is gained
What is the impulse of a force?
+equation
The change in momentum of an object
It is equal to the change in momentum of an object involved in the interaction and is also equal to the area under a force-time graph
Impulse=mv-mu
kg ms-1
Impulse=Ft
Ft=nvm-mu (data sheet)
What happens if you increase the time of contact in a collision?
the average force exerted will decrease (because the area under the graph must stay the same)
What are projectiles?
Projectiles move with a curved path because they have a combination of both horizontal motion (constant) and vertical motion which act independently (not constant)
Do you need sign convention for projectiles?
YES
What initial vertical velocity will projectiles launched upwards have?
non-zero
What do projectiles accelerate vertically at?
-9.8ms-2
What is the equation for vertical and horizontal components of the velocity?
vertical v=vsinx
horizontal v=vcosx
v acting at angle to vh can be worked out using pythagoras
what is the vertical velocity at the top of the projectile?
0ms-1 as there is a change in direction
what is the final vertical velocity equal to?
the initial vertical velocity but the opposite sign
What does G=
universal constant of gravitation (6.67x10^-11m^3kg^-1s^-2)
not the same as g
What is gravitational field strength g?
the amount of force applied to each 1kg of mass (by a gravitational field)
What do you need to remember when doing a gravitational force of attraction question with planets?
the radius of each planet
What does the r= in gravitational force of attraction questions?
distance
Experiment to measure acceleration due to gravity
F=ma
w=mg
electronic timer
height
timing plate
ball
clamp stand
The timer starts when the ball is released and stops when the ball reaches the timing playe
What is the gradient of a graph plotted with 2s (y) against t^2 (x)
9.8 (gravity)
What does it mean if 2 things are in the same reference frame?
They are moving at the same velocity (speeding and direction)
What does it mean if something is moving relative to you?
It is in another reference frame
What are einstein’s 2 postulates of special relativity?
1-when 2 observers are moving at constant velocities to one another, they will observe the same laws of physics
2-the speed of light (in a vacuum) is the same for all observers in all reference frames
What is time dilation?
a difference (increase) in a time interval as measured by a ‘stationary’ observer and a moving observer
what is t and t prime? and v
t-time measured by an observer in the same reference frame as the event
-proper time
t prime-time measured by an observer in a different reference frame to the event
-dilated time
v-speed of relative motion between 2 reference frames
What is length contraction?
A difference (decrease) in length as measured by a ‘stationary’ observer and a moving observer
what is l, l primer and v?
l-proper length
l prime-contracted length
v-speed of relative motion between 2 reference frames
what is c?
speed of light
