SP2: motion & forces Flashcards
(75 cards)
1
Q
scalar
A
a quantity with size/magnitude only
2
Q
examples of scalar quantities
A
speed, mass, distance
3
Q
vector
A
a quantity with both size and direction
4
Q
examples of vector quantities
A
force, velocity, displacement
5
Q
magnitude
A
the size of a physical quantity
6
Q
displacement vs distance
A
distance: how far an object moves displacement: difference from object’s starting point to final point
7
Q
what is speed?
A
the distance an object travels per unit of time
8
Q
typical speed for walking
A
1.5 m/s
9
Q
typical speed for running
A
3 m/s
10
Q
typical speed for cycling
A
6 m/s
11
Q
typical speed for cars
A
13-30 m/s
12
Q
typical speeds for trains
A
50 m/s
13
Q
typical speeds for aeroplanes
A
250 m/s
14
Q
speed of sound in air
A
330 m/s
15
Q
how to calculate average speed in a journey
A
total distance/total time
16
Q
different ways to measure speed:
A
-ruler & stopwatch
-light gates (connected to timer & size of object measured with ruler)
-video analysis (distance moved from frame to frame observed on a ruler in video & time between frames)
17
Q
what is the most accurate way to measure speed?
A
light gates
18
Q
what is velocity?
A
speed in a given direction
19
Q
what does a horizontal line on a distance-time graph represent?
A
stationary object
20
Q
what does a sloping line show on a distance time graph?
A
the object is moving
21
Q
what is acceleration?
A
the rate at which velocity changes
22
Q
what is acceleration measured in?
A
m/s²
23
Q
acceleration in freefall
A
10 m/s²
24
Q
typical acceleration when running
A
2 m/s²
25
typical acceleration of a family car
1-7 m/s²
26
typical acceleration of a motorbike
1-10 m/s²
27
typical acceleration of a rollercoaster
30-60 m/s²
28
typical acceleration of a formula one car
49 m/s²
29
what does a sloping line mean on a velocity/time graph?
the object is accelerating
30
what does a horizontal line on a velocity-time graph represent?
constant velocity
31
how to find the distance travelled on a velocity time graph?
area under the graph
32
how to find out acceleration on a velocity time graph?
draw a tangent on a curved line & measure the gradient
33
motion equation
v² - u² =2ax
v = final velocity
u = initial velocity
a = acceleration
× = displacement
34
how can the motion equation be used?
can be rearranged to find initial velocity, final velocity, acceleration & displacement
35
what happens when an object moves in a circle at a constant speed?
it's direction constantly changes, this change in direction causes a change in velocity, this change in velocity results in acceleration
36
how does acceleration happen in
circular movement?
if a resultant force acts on it (centripetal force) for the object moving in a circle, which acts towards the middle of the circle
37
gravitational attraction
provides the centripetal force that keeps satellites in orbit around planets and planets orbiting around the sun
38
newton's first law
an object remains in the same state of motion unless a resultant force acts on it
39
resultant force
a single force that has the same effect as all the forces acting on the object
40
what is uniform speed?
motion at a constant speed
41
uniform motion example (car)
car travels at constant velocity when driving force from engine is balanced by resistant forces like friction & air resistance
42
what is non-uniform motion?
motion with a change in speed, direction, or both
43
non-uniform motion example
at the start of a run, a runner experiences less air resistance than their thrust so they accelerate
44
newton's second law
force = mass x acceleration
(triangle = FMA)
45
how does acceleration change because of mass and resultant force?
-the acceleration of an object increases if the resultant force on it increases
-acceleration increases if the mass of the object decreases
46
intertial mass
how difficult it is to change the velocity of an object
47
inertial mass formula
force/acceleration
48
what sign do estimations need?
≈
49
practical: investigating force, mass & acceleration
1. cut an interrupt card to a known length (such as 10 cm) and attach it to an air track glider
2. set up the equipment as shown in the diagram. make sure that the air track is level, and that the card will pass through both gates before the masses hit the floor
3. set the data logging software to calculate acceleration
4. Use scales to measure the total mass of the glider, string and weight stack. record this value.
5. attach the full weight stack (6 × 10g
masses) to the end of the string
6. make sure the glider is in position and switch on the air blower. the glider should accelerate. remove one weight and attach it to the glider using blu-tack. this will keep the total mass constant
7. repeat steps 6-7 removing one weight from the stack each time. remember to attach each weight to the glider as it is removed from the weight stack
50
newton's third law
for every action there is an equal and opposite reaction
51
forces acting on a cat sat on the ground
(gravitational forces)
the cat pulls the earth up the earth pulls the cat down
(these forces are equal in size and opposite in direction)
52
weight equation
mass × gravitational field strength
53
what is weight measured in?
N (newtons)
54
what is gravitational field strength measured in?
N/kg
55
what is the relationship between weight and mass?
-they are directly proportional
-the greater the mass of the object, the greater its weight is
56
what is gravity on earth?
10 N/kg
57
what is momentum?
-the product of mass and velocity
-a vector quantity
58
how to calculate momentum (p)?
mass × velocity
59
what is conservation of momentum?
total momentum before an event = total momentum after the event (as long as no outside forces are acting on that system)
60
what happens when a resultant force acts on a moving object?
momentum changes
61
the purpose of seatbelts
-stops tumbling
-strong enough to stop you before you hit steering wheel
-slightly flexible to increase time taken for change in momentum, reducing the chance of injury
-spreads the force over a wider area of the body, reducing the pressure on any one particular part
62
the purpose of an airbag
increases time for heads momentums to reach zero, reduces force
63
crumple zone
-area at the front of the car made to be crushed in the case of a crash and to take a lot of the impact
-increases time taken to change momentum of drivers & passengers in a crash & reduces the forces involved
64
what is stopping distance? (equation)
thinking distance + braking distance
65
what is thinking distance?
the time it takes for a driver to apply the brakes after realising they need to
66
what is braking time?
the time it takes for the brakes to stop the vehicle
67
what is the average reaction time?
0.2-0.9 seconds
68
what can reaction times be affected by?
tiredness, drugs, alcohol, distractions
69
what can braking distances be affected by?
-poor roads & weather conditions
-poor vehicle conditions
-more mass in the vehicle
70
how does a car brake?
1. force applied to the brakes of a vehicle
2. work done by the friction between the brakes and the wheel
3. reduces the kinetic energy of the vehicle & slows it down
4. causes the temperature of the brakes to increase
71
faster vehicle equals…
greater braking force needed to stop it & greater deceleration
72
what can large decelerations lead to?
brakes overheating and/or loss of control
73
work done
force x distance
74
KE
1/2 x mass x v²
75
are kinetic energy and work done the same?
yes
