The answer will depend on the variables plotted on the graph!
acceleration
A straight line.
change in velocity
Magnitude of acceleration (but conveys no informationregarding acceleration's direction).
a) A circle is not the graph of a function. b) A circle is not linear.
acceleration
Indirectly, yes. If the graph is a straight line there is no acceleration, if the graph is not linear there is acceleration.
A straight line.
The slope of a speed-time linear graph represents acceleration. It indicates how quickly the speed of an object is changing over time.
One of the most common ways to represent linear equations is to use constants. You can also represent linear equations by drawing a graph.
The slope of a velocity-time graph represents acceleration.
change in velocity
Not necessarily. The equation of a projectile, moving under constant acceleration (due to gravity) is a parabola - a non-linear equation.
The slope of a velocity-time graph represents acceleration.
To find acceleration from a speed-time graph, you need to calculate the slope of the speed-time graph. The slope at any point on the speed-time graph represents the acceleration at that specific time. If the speed-time graph is linear, then the acceleration will be constant. If the speed-time graph is curved, you can find the acceleration by calculating the slope of the tangent line at a specific point.
Magnitude of acceleration (but conveys no informationregarding acceleration's direction).
Magnitude of acceleration (but conveys no informationregarding acceleration's direction).