Which statement about acceleration is always true? a
Either a change in speed or a change in direction means there is acceleration.
b
Both speed and direction must change for acceleration to occur.
c
The unit m/s is the SI unit o acceleration.
d
For objects to accelerate, they must speed up.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

there are two significant figures.

the pseudoscience are like beliefs, theories, or like practices that are considered scientific