Phyics Ib
THIS FILE DOWNLOADED FROM THE IB NOTES SITE: http://ibnotes.tripod.com/ TOPIC 2— MECHANICS FOUNDATIONS:
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Displacement— A measured distance in a given direction— tells us not only the distance of an object from a particular reference point, but also the direction from the reference point— is a vector.
Velocity— Is speed in a given direction, and is also a vector.
Acceleration— is the rate of change of velocity in a given direction (velocity/time). The unit in SI is metres per second per second, or ms-2. Is also a vector.
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Motion can be ‘relative’, ie. taken from a different reference point. The determination of speed, and also velocity and acceleration depends on what it is measured to.
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Speed and velocity can be both ‘instantaneous’ and ‘average’ Average is the speed taken over a certain time period, but Instantaneous is the speed taken at a certain point:
∆s
vav =
∆t
The instantaneous speed is given as the limit of this, or the derivative.
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Both displacement-time and velocity-time can be graphed— the area under a velocitytime graph is the displacement (when both positive and negative areas are graphed).
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Linear Motion with Constant Acceleration:
There are 4 equations for this type of momentum:
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v = u + at — The definitions of accleration. If a body starts from rest then its speed after time t will be given by v = at. If its initial speed is u then this equation applies.
1
s = ut + at2 — The distance travelled is the area under the speed-time graph
2
1 and the body starts from rest, then s = vt2. But if the body starts from speed
2
u then we must add the area ut. v2 = u2 + 2as
— We can eliminate the time from the last equation by v–u . We eventually end up with this equation. substituting in t = a (u + v) s= t
2
Acceleration due to free fall is called the acceleration due to gravity. It is denoted g in SI, and is usually given the value 9.8 ms-2.
NOTES BY JAMES
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•
•
Displacement— A measured distance in a given direction— tells us not only the distance of an object from a particular reference point, but also the direction from the reference point— is a vector.
Velocity— Is speed in a given direction, and is also a vector.
Acceleration— is the rate of change of velocity in a given direction (velocity/time). The unit in SI is metres per second per second, or ms-2. Is also a vector.
•
Motion can be ‘relative’, ie. taken from a different reference point. The determination of speed, and also velocity and acceleration depends on what it is measured to.
•
Speed and velocity can be both ‘instantaneous’ and ‘average’ Average is the speed taken over a certain time period, but Instantaneous is the speed taken at a certain point:
∆s
vav =
∆t
The instantaneous speed is given as the limit of this, or the derivative.
•
Both displacement-time and velocity-time can be graphed— the area under a velocitytime graph is the displacement (when both positive and negative areas are graphed).
•
Linear Motion with Constant Acceleration:
There are 4 equations for this type of momentum:
•
•
•
•
•
v = u + at — The definitions of accleration. If a body starts from rest then its speed after time t will be given by v = at. If its initial speed is u then this equation applies.
1
s = ut + at2 — The distance travelled is the area under the speed-time graph
2
1 and the body starts from rest, then s = vt2. But if the body starts from speed
2
u then we must add the area ut. v2 = u2 + 2as
— We can eliminate the time from the last equation by v–u . We eventually end up with this equation. substituting in t = a (u + v) s= t
2
Acceleration due to free fall is called the acceleration due to gravity. It is denoted g in SI, and is usually given the value 9.8 ms-2.
NOTES BY JAMES