constant speed
Constant speed ... zero acceleration.
The straight horizontal line on the graph says: "Whatever time you look at, the speed is always the same". This is the graph of an object moving with constant speed.
Acceleration
If a graph shows distance on the vertical axis and time on the horizontal axis, and the speed is steadily increasing, the line representing speed will be a straight line.
No. If the horizontal axis is time, and the vertical axis is speed, and you're standing still,Then the graph is perfectly horizontal, and it coincides with the horizontal axis.
constant speed
The given speed is constant for the given period
Constant speed ... zero acceleration.
The straight horizontal line on the graph says: "Whatever time you look at, the speed is always the same". This is the graph of an object moving with constant speed.
Acceleration
If a graph shows distance on the vertical axis and time on the horizontal axis, and the speed is steadily increasing, the line representing speed will be a straight line.
The horizontal axis is for the independent variable, which is time. Time is always placed on the horizontal, or x-axis.
The horizontal axis of a typical graph would be the "X-axis"
The graph you described is a speed-time plot. If the line is horizontal, that indicates no change in speed over time. In other words, there is no acceleration (acceleration is zero), since there is no change in speed.
Speed = distance / time A line graph with distance on the vertical axis and time on the horizontal axis could be used to determine speed. The speed would equal the slope of the line. Alternatively, a line graph with distance/time on the vertical axis and time on the horizontal axis would show speed. The acceleration would equal the slope of the line.
The line would indicate motion at a constant speed.