Forces And Motion Flashcards
1
Q
Scalar quantity
A
A quantity that only a magnitude
2
Q
Vector quantity
A
A quantity with both a magnitude and direction
3
Q
List scalar quantities
A
Speed, mass, distance, time, energy, temperature
4
Q
List vector quantities
A
Velocity, force, displacement, acceleration, momentum
5
Q
What is distance, its symbol and units?
A
- distance = how far an object has traveled with no regard to direction
- symbol = d
- units = meters (m)
6
Q
What is displacement, its symbol and units?
A
- displacement = the distance an object has traveled in a certain direction
- symbol = s
- units = meters (m)
7
Q
What is speed, its symbol and units?
A
- speed = a measure of how fast an object is travelling
- symbol = s
- units = meters per second (m/s)
8
Q
Formula for average speed
A
Average speed = total distance/ total time
9
Q
What is stopping distance?
A
Total distance travelled during the time it takes for the vehicle to come to a stop
10
Q
What is stopping distance consisted of?
A
Thinking distance and braking distance (in that order!)
11
Q
What is thinking distance?
A
Distance travelled during the time it takes for the driver to react
12
Q
What is braking distance?
A
Distance travelled whilst the brakes are being applied
13
Q
Stopping distance formula
A
Stopping distance = thinking distance + braking distance
14
Q
Do factors affecting TD affect the driver or the vehicle?
A
Driver
15
Q
Do factors affecting BD affect the vehicle or the driver?
A
Vehicle
16
Q
Factors affecting thinking distance
A
- Speed of the car
- drugs + alcohol
- tiredness
- some medications
- caffeine
17
Q
Factors affecting braking distance
A
- speed of the car
- icy/wet roads (reduce traction)
- old worn tires (reduce traction)
- overloaded cars (stopping power has to increase so it will take longer to stop)
18
Q
What does stationary look like on D-T graphs?
A
Gradient = 0 , horizontal line
19
Q
What does moving forward look like on D-T graphs?
A
Positive gradient, upwards slope
20
Q
What does moving backwards look like on Đ-T graphs?
A
Neagtive gradient, downwards slope
21
Q
What does in front/ behind the starting point look like on D-T graphs?
A
- in front = above x-axis
- behind = below x-axis
22
Q
What does moving fast look like on D-T graphs?
A
Steep gradient
23
Q
What does moving slow look like on D-T graphs?
A
Shallow gradient
24
Q
What does constant speed look like on a D-T graph?
A
Straight line
25
What does acceleration/deceleration look like on D-T graphs?
Curved line
26
What is gradient equivalent to on D-T graphs?
Speed
27
Gradient formula
Change in Y / change in X
28
Describe the investigating speed experiment
- roll a marble down a ramp with a clamp and stand attached to it
- record time taken for marble to roll down the ramp
- repeat 3 times for an average time
- measure the length of the ramp using a ruler
- divide total distance of ramp by total time taken to obtain average speed of marble
- repeat again with altered height in even increments
29
describe some systematic and random errors that could occur in the investigating speed experiment
- SE = not reading the length of ramp off ruler at eye-level = parallax error
- SE = not using a light gate to measure time taken but use a stopwatch = includes human reaction time, so not completely accurate result
- RE = ensuring that there is no environmental chanegs to area during repeats e.g no wind, surface remains same
30
Constant velocity on V-T graph
Horizontal line
31
Acceleration on V-T graph
equivalent to the gradient
32
Deceleration on V-T graph
Negative gradient
33
Positive velocity V-T graph
Above x-axis
34
Negative velocity on V-T graph
Below x-axis
35
What is gradient equivalent to on a V-T graph?
Acceleration
36
How do you find distance travelled on a V-T graph?
Use the ‘counting squares method’ and find the area under the graph
- find the area of one square
- count the number of squares
- multiply the values together
OR use the formula s = 1/2 x (v+u)t
37
Average velocity formula
Displacement/ time OR v + u / 2
38
Define acceleration
The rate of change in velocity, meaning that an object’s velocity will increase by x meters per second, every second
39
Acceleration units
Meters per second squared (m/s2)
40
Deceleration
Deceleration is slowing down, basically negative acceleration. So if an object is decelerating, its acceleration is always negative as the final velocity will always be smaller than its initial one
41
Acceleration formula
a = v - u / t
42
what are the three suvat equations we need to know?
SAT = the one w/o displacement, the one w/o acceleration, the one/wo time
43
name the SAT equations
- no S; v = u + at
- no a; s = 1/2 x (u+v)t (can be used for finding displacement using area under a V-T graph)
- no t; v2 = u2 + 2as
44
what is a force?
a force is a push or pull
45
formula to calculate weight
weight (w) = mass (m) x gravitational field strength (g)
46
what are the three things that forces can change about an object?
- change in speed
- change in direction
- change in shape
47
name the 9 types of forces + effects
- weight (gravitational) = pulls objects down: W=mg
- normal reaction force = support force from surfaces, acts upward
- friction = opposes motion between surfaces
- air resistance = friction from air, opposes motion
- tension = pulling force in ropes/strings
- upthrust = upward force from liquids/gases
- magnetic = force between magnets or magnetic materials
- electrostatic = force between charged objects
- applied force = force applied by a person or object
48
is force scalar or vector quantity? why is this?
force is a vector quantity as it has both a magnitude and direction
49
what is newton's first law?
- explains what happens to objects when forces are balanced:
- no resultant force = constant motion
- this means that stationary objects will remain stationary OR objects will keep moving at a constant speed in a constant direction (continue moving at a constant velocity)
50
what is resultant force? what are the three main rules for calculating them?
- resultant force = the single overall force that describes the combined motion of all the forces acting on a system
- when forces act in opposite direction, subtract to get resultant force
- when forces act in the same direction, add them to get resultant force
- when they act perpendicularly to each other, then use Pythagoras' theorem to calculate resultant force
51
what is friction?
- friction is a resistive force that opposes motion between surfaces
- it happens due to microscopic irregularities on the surfaces that rub against each other and oppose their motion
52
what is newton's second law?
- explains what happens when forces are not balanced (resultant force is greater than 0)
- when forces are unbalanced, a resultant force is created, which causes acceleration
- F = ma, where F ∝ a when mass remains constant
- this is because acceleration can only occur if there is a force present
53
how are newton's first and second law related?
newton's first law is essentially a special case of newton's second law that explains what happens when forces are balanced
54
formula for resultant force
resultant force (F in N) = mass (m in Kg or g) x acceleration (a in m/s sq)
55
what is the value of acceleration of freefall?
- freefall is when an object falls solely due to gravity and nothing else
- on earth, as gravity is 9.8N/kg, acceleration due to gravity in freefall is 9.8m/s2
56
what is newton's third law?
- every action has an equal and opposite reaction
- forces always act in force pairs - the pairs of forces that act between two objects
57
what is the criteria that a force pair must meet to obey newton's third law?
- force pairs must meet ALL of the below criteria to obey newton's third law
- they must both be the same type of force
- they must have the same magnitude (equal in size)
- they must act in opposite directions
- they must act on different objects
58
describe the forces acting on a falling skydiver and why he reaches terminal velocity
- the instant he jumps out the plane = there is no longer a support force from the plane's floor, so the only force acting is his weight
- this causes him to reach maximum acceleration due to gravity (9.8 m/s²) , causing the resultant force = weight
- as he speeds up, drag increases, decreasing F (F = weight - drag)
this means he accelerates at a slower rate
- eventually, drag increases to balance weight, causing F= 0 ( as W = D so when W - D, F = 0)
- this means no acceleration, causing him to fall at a constant terminal velocity
- when the parachute open, drag increases to greater than weight due to the parachute's large SA, causing a negative resultant force (W
59
describe what a V-T graph would look like for the skydiver falling
- the overall shape is a wave
- 1 - a = 9.8 (max. acceleration - freefall due to gravity, only W acting)
- 2 - a < 9.8 (D increases, F decreases ∴ skydiver accelerates at a slower rate)
- 3 - a = 0 (W = D ∴ F = 0)
- 4 - a < 0 (parachute opens = D>W ∴ -F = -a so deceleration)
- 5 - a = 0 (slows down: D=W ∴ F = 0 = a, so new slower + safer terminal velocity achieved)
- 6 - a = 0 (hits the ground so no longer in motion)
60
how does surface area affect drag?
- as SA increases, drag increases
- larger area facing the air flow, so more air is displaced = increased air resistance
61
explain why a block with identical mass but smaller surface area would sink to the bottom of a measuring cylinder of glycerol faster
- they both have the same weight, and same initial acceleration of 9.8m/s²
- however, the block with the smaller SA has a smaller initial drag (and so smaller rate of increase in drag)
- this means that it takes longer for the W=D as the object must spend longer accelerating to do so (as drag increases with speed)
- the object spends longer accelerating in order to do this ∴ reaches a faster terminal velocity later than the other block, causing it to sink to the bottom earlier
62
explain why a block with identical surface area but greater mass would sink to the bottom of a measuring cylinder of glycerol faster
- both objects have the same SA and same initial acceleration of 9.8m/s²
- as they speed up, the rate of drag would increase equally for both as they have the same surface area and initial acceleration
- however, as one block has a larger weight, it takes longer for drag to balance it
- so the object spends longer accelerating in order to do this ∴ reaches a faster terminal velocity later than the other block, causing it to sink to the bottom earlier
63
what does Hooke's law state?
The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality
64
what is the formula for Hooke's law? name the units for each value involved
- Force (F) = k (spring constant) x e (extension)
- F ∝ e as long as k remains constant
- F is measured in newtons (N)
- k is measured in N/m
- e is measured in m
65
describe and explain the parts of a force-extension graph
- linear section - obeys Hooke's law ∴ demonstrating elastic behavior
- curved section - disobeys Hooke's law ∴ demonstrates plastic behaviour
- point between curved and linear bit - limit of proportionality where the object undergoes plastic deformation
66
what does it mean if there is a shallow gradient on a force-extension graph? what does it mean if there is a steep gradient?
- shallow gradient = stretchy
- steep gradient = stiff
67
