Speed and Velocity 1
Speed (or velocity) = Distance / Time
Velocity is the same as speed, but in a given direction. To calculate velocity, use the above equation. Velocity is measured in metres per second (north, or appropriate direction).
On a distance-time graph-
-When an object is stationary, the line is horizontal
-When an object is moving at a constant speed, the line is a diagonal slope
-The steeper the line, the greater the speed of the object
-If something is returning back to its original place, the lines that represent it are ones that slope downwards
-A steepening curve represents speeding up
-A levelling off curve represents slowing down
Speed and Velocity 2
The velocity of an object is its speed in a given direction.
In a velocity-time graph-
-The gradient is the acceleration
-Steady speed is represented by a horizontal line
-The steeper the line, the greater the acceleration (or deceleration)
-The area under the graph is equal to the distance travelled in that time interval
-A curve means changing acceleration
-Speed is found by reading the value on the y-axis
Acceleration = Change in Velocity / Time taken
Acceleration is how quickly the velocity of an object is changing. The unit of acceleration is m/s squared. And because this is an extra hard topic, here is an example:
A snail (haha, good one uma) accelerates steadily from 2 m/s to 6 m/s in 5.6 seconds. What is it's acceleration?
Acceleration = Change in velocity / time taken
= ( 6 - 2 ) / 5.6 = 4 / 5.6
= 0.71 m/s squared
d change in v
s x t a x t
Newtons 1st Law of Motion
Balanced forces mean no change in velocity
Basically, as long as the forces of an object are balanced, it will just stay still, unless it is moving, in which case it will continue moving at the same velocity.
When something is moving at a constant velocity, all the forces acting on it must be balanced.
To continue moving at a constant speed, there must be zero resultant force, not a constant overall force.
Newtons 2nd Law of Motion
A resultant force means acceleration
If there is an unbalanced force, the object will accelerate in that direction.
This acceleration can take five different forms; starting, stopping, speeding up, slowing down and changing direction. On a force diagram, the arrows will be unequal.
- the bigger the force, the greater the acceleration/deceleration
- the bigger the mass, the smaller the acceleration
- to get a big mass to accelerate as fast as a small mass, it needs a bigger force
Resultant Force = Mass x Acceleration
In most real situations, there are at least two forces acting on an object. The overall effect of these forces will decide the motion of the object. This overall force is called the resultant force.
Newtons 3rd Law of Motion
If object A exerts a force on object B, then object B will exert the exact opposite force on object A.