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Physics > Chapter 7 > Flashcards

Chapter 7 Flashcards

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1
Q

What is displacement

A

The distance in a given direction

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2
Q

Speed

A

The defund as change of distance per unit time

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3
Q

Velocity

A

The defined as change of displacement per unit time. In other words velocity is speed in a given direction.

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4
Q

Speed equation

A

Speed = s / t

Speed = v 
Distance = s
Time = t
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5
Q

Distance travelled

A

S = v x t

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6
Q

Instantaneous speed

A

Tangent speed at an instant in time.

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7
Q

Average Speed

A

Straight line from start to end
Speed over a period of time

Y axis distance
X axis time
Distance = s
Time = t

S₂ - S₁ / T₂ - T₁

Average speed = S/T

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8
Q

Circular motion

A

In a circular motion speed is constant but as the direction is always changing V is always changing
So we say that the object is accelerating

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9
Q

Acceleration is defined what?

A

Defined as the change of velocity per unit time

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10
Q

Unit of acceleration

A

Ms-²

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11
Q

Acceleration equation

A

Change of velocity / time taken

V-U / T

Rearrange
V = u+ AT

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12
Q

Non uniform acceleration

A

Non uniform acceleration is where the direction of motion of an object changes or it’s speed changes at a varying rate.
Acceleration = gradient of the line on the velocity-time graph

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13
Q

Final velocity measurement

A

Ms - ¹

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14
Q

Initial velocity

A

Ms -¹

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15
Q

Time

A

Seconds

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16
Q

Velocity time graph

A

Slope which goes down straight diagonal

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17
Q

Acceleration from a V-T graph

A

Curve graph which needs a tangent

V2 - V1 / T2 - T1

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18
Q

Displacement from a V-T graph

A

Triangle and rectangle boxes

S= (1/2 x t1 x v1) + ((t2-t1) x v1)

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19
Q

Suvat equation

Without S

A

V= u + at

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20
Q

Suvat equation

Without A

A

S= u+v/2 x t

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21
Q

Average velocity

A

U+V/2

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22
Q

Suvat equation

Without V

A 
S= u x T + (1/2) x a x T²
Rearrange to find T 
√S / a x 1/2 = T
Rearrange to find S 
S= u x T + 1/2 x 9.8 x (0.9²)
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23
Q

Suvat equation

Without u

A

S= v x T - (1/2) x a x T²

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24
Q

Suvat equation

Without T

A

V² = u² + 2 x a x s

25
Q

Weight = what?

A

Mass x gravity

26
Q

Force = what?

A

Mass x acceleration

Newtons second law

27
Q

Free fall info

A

Heavy objects typically fall faster in air vac use air resistant = cross sectional area = r²

Weight = mass = volume = r³

28
Q

Distance time graph

A

Wave going up then down then up

Like a transverse wave but going up

29
Q

Displacement time graph

A

Goes up then down like a shape of a hill

30
Q

Speed time graph

A

V shape graph that is a straight line
Example
Going from 10 on the y axis to 0 on the y axis and then going back up in a straight line but NOT virtual diagonal line

31
Q

Velocity time graph

A

Y axis going from POSITIVE to NEGATIVE a straight line down diagonally

32
Q

What happens to distance

A

If distance increases with time as there isn’t really any such things as negative distance due to its scalar nature

33
Q

Why does displacement end at zero

A

It ends a zero due to its vector nature. This plots a similar parabola y = -ax² + bx + c

34
Q

Why does velocity have a constant negative gradient

A

This is because of -9.81 ( gravity) and the displacement when v>0 = displacement when v<0 ( area under line)

35
Q

Speed time graph

Gradient = what ??

A

Velocity

Δy/Δx =Δs/T = velocity

36
Q

Velocity time graph
Gradient = what ??
Area = what ??

A
  1. Acceleration
  2. displacement

Δy/Δx = Δv/T = acceleration

Y x X = v x T = displacement

37
Q

Projectile motion

A

Projectile motion = horizontal motion + vertical motion

38
Q

Projectile motion info 1

A

Horizontal place we simply use v=s/T as there is no acceleration

39
Q

Vertical plane

A

Treated as a free fall question

40
Q

Example question

A 
Vertical = Suvat 
Horizontal = v=s/T 
So for horizontal you need the horizontal line from the triangle and the Suvat answer
Suvat = T
Horizontal = s
41
Q

Constant speed of a circle

A

V = 2 x π × r / T

Where T is the time to move round once and 2 x π x r is the circumference of the circle.

42
Q

Acceleration is defined …

A

As charge of velocity per unit time

43
Q

Uniform acceleration

A

Uniform acceleration is where the velocity of an object moving along a straight line changes at a constant rate. In other words the acceleration is constant.

A= v-u / t
V = initial
U = final
44
Q

Constant velocity

A

Speed y axis
Time x axis

When an object is moving at a constant velocity.
S = v x t
Straight line horizontal

45
Q

Constant acceleration

A 
Speed = y axis 
Time = x axis

Consider an object at constant acceleration (a) from initial velocity (u) to velocity (v) at time (t)
Equation = s= (u+v) x t / 2 (Suvat equation )
Graph
Diagonal line from lowest point on y axis to the highest point on x axis
Middle of y axis is the average speed

46
Q

Changing acceleration

A

When an object is changing acceleration, let v represent the velocity at time t and (v+δv)
(δ = delta )
Represent the velocity a short time later at (t+δt).

Graph
So it’s a (s) graph but the (s) is horizontal
V+δv is above v
So is the same with time

Displacement = area under the line of velocity time graph
Example like a constant velocity
Area = (6 y axis) x (5 x axis) = 30m
Distance = 30m

47
Q

Does a heavy object fall faster than a lighter object.

A

Release a stone and a small coin at the same time. Which one hits
ine ground first? The answer to this question was first discovered by
calileo Galileli about tour centuries ago. He reasoned that because any
number of identical objects must fall at the same rate, then any one
such object must tall at the same rate as the rest put together. So he
concluded that any two Objects must fall at the same rate, regardless
of their relative weights.

48
Q

The difference between distance - time graph and a displacement - time graph
Part 1

A

Displacement is distance in a given direction from a certain point.
Consider a ball thrown directly upwards and caught when it returns.
If the ball rises to a maximum height of 2.0 m, on returning to the
thrower its displacement from its initial position is zero. However, the
distance it has travelled is 4.0 m.

Graph 
Semi circle graph 
Y axis = displacement 
X axis = time 
Highest point is the maximum point

Immediately after leaving the thrower’s hand, the velocity is
positive and large so the gradient is positive and large.

As the ball rises, its velocity decreases so the gradient decreases.

At maximum height, its velocity is zero so the gradient is zero.

As the ball descends, its velocity becomes increasingly negative,
corresponding to increasing speed in a downward direction. So the
gradient becomes increasingly negative.

49
Q

The difference between distance - time graph and a displacement - time graph
Part 2

A

Distance graph

The distance travelled by the object changes with time as shown
by Figure 2. The gradient of this line represents the speed. From
projection to maximum height, the shape is exactly the same as in
Figure 1. After maximum height, the distance continues to increase so
the line curves up, not down like Figure 1.

Graph
Y axis = distance
X axis = time
First half of the graph slowly projects upwards then the second half it projected further upwards
Half way of the graph before being projected upwards half way is the maximum height
Looks like a horizontal (s).

50
Q

The difference between speed - time graph and a velocity - time graph
Part 1

A

Velocity is speed in a given direction. Consider how the velocity of
an object thrown into the air changes with time. The object’s velocity
decreases from its initial positive (upwards) value to zero at maximum
height then increases in the negative (downwards) direction as it falls.

51
Q

The difference between speed - time graph and a velocity - time graph
Part 2

A

1
The gradient of the line represents the object’s acceleration
This is constant and negative, equal to the acceleration ot free fall, q.
The acceleration of the object is the same when it descends as when
it ascends so the gradient of the line is always equal to -9.8 ms-2
2
The area under the line represents the displacement of the
object from its starting position.
The area between the positive section of the line and the time
axis represents the displacement during the ascent.
The area under the negative section of the line and the time
axis represents the displacement during the descent.

Taking the area for a as positive and the area for b as negative, the
total area is therefore zero. This corresponds to zero for the total
displacement.

Graph
Positive to negative for y axis
Maximum height occurs at time t = u / g

52
Q

Projectile

A

A projectile is any object acted upon only by the force of gravity

53
Q

Projectile 1

A

The acceleration of the object is always equal to g and is always downwards because the force of gravity acts downwards.
The acceleration therefore only affects the vertical motion of the object.

54
Q

Projectile 2

A

The horizontal velocity of the object is constant because the acceleration of the object does not have a horizontal component.

55
Q

Projectile 3

A

The motions in the horizontal and vertical directions are independent of each other.

56
Q

Vertical projectile

A

Such an object moves vertically as it has no horizontal motion. Its acceleration is 9.8 ms-2 downwards. Using the direction code + is
upwards, - is downwards, its displacement, y, and velocity, v, after time t are given by
V=u - gxt
y=uxt - 1/2 x gxp

57
Q

Horizontal projected

A

A stone thrown from a chilf top follows a curved path downwards before it hits the water. If its initial projection is horizontal its path through the air becomes steeper and steeper as it drops

the faster it is projected, the further away it will fall into the sea

the time taken for it to fall into the sea does not depend on how
fast it is projected.

Suppose two balls are released at the same time above a level
floor such that one ball drops vertically and the other is projected
horizontally. Which one hits the floor first? In fact, they both hit the
floor simultaneously.

They are both pulled to the ground by the force of gravity, which
gives each ball a downward acceleration g. The ball that is projected horizontally experiences the same downward acceleration as the other
ball. This downward acceleration does not affect the horizontal motion
of the ball projected horizontally - only the vertical motion is affected,

58
Q

The effects of air resistance

A

The effects of air resistance

A projectile moving through air experiences a force that drags on it
because of the resistance of the air it passes through. This drag force is
partly caused by friction between the layers of air near the projectile’s
surface where the air flows over the surface.
The drag force:

acts in the opposite direction to the direction of motion of the
projectile, and it increases as the projectile’s speed increases

has a horizontal component that reduces both the horizontal speed
of the projectile and its range

reduces the maximum height of the projectile if its initial direction is above the horizontal and makes its descent steeper than its ascent.

Physics (19 decks)

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