Check out this link and play around with it and have a go at contructing circuits...
DC CIRCUIT SIMULATION
There are plenty of other good educational (and FUN) simulations to play around with...
SCIENCE SIMULATIONS FROM THE UNIVERSITY OF COLORADO
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Tuesday, August 31, 2010
Thursday, August 19, 2010
Forces and Mechanics for Year 10 Sia1 and 11 PY
At it's simplest a Force, symbol F can be seen as a push or a pull in a given direction. From this we can see that Force must be a Vector Quantity as it has a direction and also has a magnitude.
The Net Force, Fnet is the resultant sum of all the vector forces acting on a body and if these are balanced then Fnet is zero and the body is subject to Newton's First Law of Motion, ie it has inertia and remains in equilibrium:
- if it is at rest it will continue to remain at rest (be stationary) and if it is moving it will continue to move at a constant speed
- all the force vectors must add up to zero
If the forces become unbalanced the Fnet no longer add to zero and the the object starts to accelerate or decelerate, according to Newton's Second Law of Motion (Force = Mass x Acceleration) and the sum of all the vector forces must produce a resultant Force Vector in the direction of the acceleration.
Newton's third law can help us with understanding some of the other forces in play and how to represent them on a Force Diagram: "every action has an equal and opposite reaction." So for example if a box is sitting on the ground stationary there is a force, due to gravity, acting in a downward direction. From Newton's 3rd Law there must be an equal and opposite reaction: in this case a force acting upwards that is equal to the gravitational force: the two forces balance out with the resultant Fnett = 0, so the box remains stationary and will only move if another force acts on the box making the Fnett grater than zero. Now the forces are no longer in balance or equilibrium!
Monday, August 9, 2010
MOTION
A quick post to go over some of the main points of motion and the graphs associated with them. The first thing to get our heads around is the difference between scalar and vector quantities.
A Scalar quantity only has a magnitude whereas a Vector quantity has a direction as well as a magnitude.
For example time and distance are scalar quantities as they only have a magnitude, whereas displacement and velocity are vector quantities as they have both a magnitude and a direction:
Quantity Scalar or Vector Magnitude and Direction Unit
Displacement, as opposed to just distance, is the shortest distance form the start point and comprises a distance along with an angle or bearing, and Velocity is speed in a given direction.
On the displacement time graph, to the side, the displacment is shown by the orange arrow, which shows the shortest distance from the origin. This displacement should be given with a distance in metres as well as a direction, with an angle or bearing.
On the velocity time graph the minus figure does not indicate a minus speed; instead it indicates a direction relative to the start direction which is shown from the origin. In this example if we assume the the y axis corresponds to a direction angle of 90 degrees or East, then the initial velocity is around 45 degrees, or North East, which then changes to approximately 135 degrees and returns to a direction / angle that is the same as the origin at 30 seconds. The velocity continues on this same angle / heading for another 7 seconds or so then changes angle back to a direction of approximately 45 degrees, or North East to return to the same direction / angle / bearing as the start direction / angle / bearing at 50 sec.
A Scalar quantity only has a magnitude whereas a Vector quantity has a direction as well as a magnitude.
For example time and distance are scalar quantities as they only have a magnitude, whereas displacement and velocity are vector quantities as they have both a magnitude and a direction:
Quantity Scalar or Vector Magnitude and Direction Unit
Time Scalar Just a magnitude Seconds
Distance Scalar Just a magnitude Metres
Displacement Vector Magnitiude and Direction Metres
Velocity Vector Magnitude and Direction Metres per Second
Displacement, as opposed to just distance, is the shortest distance form the start point and comprises a distance along with an angle or bearing, and Velocity is speed in a given direction.
On the displacement time graph, to the side, the displacment is shown by the orange arrow, which shows the shortest distance from the origin. This displacement should be given with a distance in metres as well as a direction, with an angle or bearing.
On the velocity time graph the minus figure does not indicate a minus speed; instead it indicates a direction relative to the start direction which is shown from the origin. In this example if we assume the the y axis corresponds to a direction angle of 90 degrees or East, then the initial velocity is around 45 degrees, or North East, which then changes to approximately 135 degrees and returns to a direction / angle that is the same as the origin at 30 seconds. The velocity continues on this same angle / heading for another 7 seconds or so then changes angle back to a direction of approximately 45 degrees, or North East to return to the same direction / angle / bearing as the start direction / angle / bearing at 50 sec.Finally to reiterate a number of final points:
The gradient of a distance time graph equals the speed- The gradient of a velocity time graph equals the acceleration
- The area under a velocity time graph equals the distance travelled
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