Space Time And Motion Flashcards

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1
Q

When can we use suvat equation?s?

A

Motion with constant acceleration

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2
Q

What is free fall

A

Object undergoing acceleration due to gravity

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3
Q

What forces act on an object in free fall?

A

Only weight force due to gravity

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4
Q

How does the rate of free fall differ for different objects?

A

It doesn’t- all objects free fall at the same rate

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5
Q

Outline method to calculate g with a ball bearing and electromagnet

A
  • set up: electromagnet,ball bearing , timer,switch, trapdoor ,computer
  • measure height from bottom of ball to trapdoor
  • flick switch to simultaneously start timer and disconnect magnet
  • circuit breaks when ball hits trapdoor and stops timer
  • repeat three timers and take average t
  • record for diff heights
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6
Q

Outline how to evaluate data for calculating g from ball bearing and electromagnet

A
  • plot graph height against time squared
  • as initial v is zero graph is a= 1/2at^2 from suvat equations
  • gradient is 1/2g
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7
Q

How to decrease uncertainties in calculating g from ball bearing and electromagnet

A
  • small and heavy ball bearing so assume small enough air resistance to ignore it
  • small increment ruler
  • pick certain ball point to measure from to reduces random height error
  • use computer instead of stopwatch so time uncertainty smaller
  • could use light gates to automatically calculate v then use v^2=2as
  • this method does not include calculating v so could reduce systematic error
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8
Q

Outline video camera method for finding g

A
  • video camera metre ruler
  • analyse frame by frame making note of distance travellers every 0.1 secs
  • create a iterative table calculating velocity and acceleration or do gradient of velocity against time
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9
Q

Outline strobe ball method to find g

A
  • Regular camera in a dark room and a strobe light
  • set camera to long exposure and drop strobe
  • will light up at regular intervals and appear multiple times
  • calculate change in distance between each location use to find g
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10
Q

How to reduce uncertainties in video techniques to find g

A
  • measuring distance is main uncertainty
  • parallax error
  • time uncertainty reduced with smaller time intervals by increasing frequency or higher frame rate
  • repeats
  • large distance and small time increments
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11
Q

How can u find initial velocity from a velocity time graph for constant acceleration?

A

Y intercept

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12
Q

Definition for Newton’s first law

A

Body will remain at rest of moving at constant speed in a straight line unless acted on by a resultant force

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13
Q

What is Newton’s second law

A

F=ma force of an object is proportional to acceleration

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14
Q

Definition of newtons 3rd law

A

When an object a exerts a force on object b , object b exerts and equal and opposite force (of the same type) on object a

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15
Q

What is newtons 3rd law a consequence of ?

A

Conservation of momentum as resultant force means change in mass or acceleration and therefore change in momentum which must be conserved so must be equal and opposite force to conserve

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16
Q

What can be said about momentum?

A

Always conserved

Momentum before collision= momentum after

17
Q

What does elastic collision mean?

A

Kinetic energy and momentum conserved, No energy dissipated

18
Q

What is an inelastic collision?

A

Kinetic energy not conserved, dissipated to heat sound etc

19
Q

How does Newton’s second law link to momentum ?

A

Force is rate of change of momentum

F=mv/t

20
Q

When does F=ma not apply? What equation does apply.

A

When accelerating close to the speed of light mass is changing and equation no longer applys,
F=mv/t does

21
Q

What is impulse? What is it equal to

A

Impulse=Fxt= change in momentum

22
Q

What is a drag force?

A

Frictional force in liquids and gases

23
Q

What is drag force proportional to?

A

Speed

24
Q

How does shape of object affect friction/drag forces?

A

Larger surface area,less streamlined, more collisions ,greater resistive forces

25
Q

How do frictional forces affect kinetic energy ?

.

A

Convert to heat

26
Q

When does an object reach terminal velocity (in terms of forces)

A

Frictional force= driving force (no resultant force)

27
Q

How does an object reach terminal velocity

A

Object accelerates from rest, as velocity increases resistive forces increase (proportionally)
Eventually ma=to resistive forces and no resultant force so at terminal velocity

28
Q

Discuss a sky diver reaching terminal velocity?

A
  • accelerates until air resistance=weight (terminal velocity)
  • open parachute dramatic increase in surface area so increase in air resistance
  • resultant force upwards do decelerates , slows down so air resistance decreases
  • reaches new lower velocity terminal velocity which is lower enough to survive landing
29
Q

Outline method to measure terminal velocity of a ball bearing?

A
  • tube with elastic bands at fixed distances filled with viscous (thick,resistant to flow) liquid
  • drop ball record time to reach each band w stop watch
  • calculate average time gap between bands then average velocity
  • when velocity is constant it’s reached terminal velocity
30
Q

What variables can we investigate when measuring terminal velocity?

A
  • liquid: greater viscosity ,greater drag force, lower term velocity
  • change shape: greater surface area, less stream lined, greater drag , lower term velocity
  • increase mass: greater weight force, greater drag force required to balance, greater terminal velocity
31
Q

What is work done a measure of?

A

Amount of Energy transferred

32
Q

What is the definition of the joule

A

Work done equation tells us:

Work done when force of one newton moves an object one metre

33
Q

What is definition of power?

A

Rate of energy transferred

34
Q

Energy cannot be..

A

Created or destroyed only transferred

35
Q

What is the equation for efficiency in terms of energy?

A

Efficiency= (useful energy output/ total energy input ) x 100%

36
Q

When we ignore friction ( no energy dissipation) then sum of kinetic and potential energy is …..

A

Always constant