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Dynamics(sometimes called)
Kinematics
Mechanics Lecture 46th November 2014
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Dynamics(sometimes called)
Kinematics
Mechanics Lecture 46th November 2014
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Check basic definitionsScalar Vector Units
Distance
How far you have gone
Displacement
Distance from home in a given direction
m
m with direction (compass etc)
Speed
How fast you are going
Velocity
How fast you are going in a given direction
ms-1
ms-1 in specified direction
Acceleration
Rate of change of velocity vector
ms-2 in specified direction
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Speed – easy stuff…
If an object travels at constant speed v, for distance d in time t :
v = d/t so d= v t and t=d/v
If the speed does not remain constant then v=d/t represents an average speed over time t.
• This matters for speed cameras
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Graphing motion
• Mini- whiteboards –• Displacement against time• Velocity against time
• What does this graph tell us?
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Walking graphs.D
ispl
acem
ent
Time
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Walking graphs.D
ispl
acem
ent
Time
What’s the story?
Set off for the bus here
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Getting speed from distance graphs (1)
Easy! Steady speed. v = s/t
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Getting speed from distance graphs (2)
Variable speed
Need to take the tangent at the time you are interested in and find its gradient.EMPA tip – 8cm * 8cm minimum
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Graphing motion
• What does the area under a velocity/time graph give us?
• What does this graph tell us?
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Card sort
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
The equations of motion, forconstant acceleration
in a straight line
• Five parameters can describe motion…
s - displacementu - initial velocityv - final velocitya - accelerationt - time
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
These are the four “suvat” equations:
v = u + ats = ½ (u + v) ts = u t + ½at2
v2 =u2 + 2as
So each one links four of the five parameters
no sno ano vno t
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Where do these come from?
• We’ll see later! • More important that you can use
them systematically
Suvat –Systematically!
Some more practice
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Where do the suvat equations come from?
• Try to derive first two from thinking about a and s
• The third and fourth come from combining the first two
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Free Fall
• Galileo’s ideas
• How to examine using modern methods?
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Graph this (in Excel)
• ..\..\..\..\A levels\A level Physics\AS Physics\Unit 2\Dynamics\graph for NT book freefall data.xlsx
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Using suvat with free-fall equations
Using suvat with free-fall equations - practice
Objectives• Define basic
parameters• Describe motion
graphically• Derive two SUVAT
equations
Key WordsDistance / DisplacementSpeed / VelocityAccelerationSUVAT
Summary
• Four suvat equations
• Link the five parameters s u v a t
• Easy to use if you are systematic and consistent with coordinate systems.
• Unlikely to be tested on derivation