Read through the materials "Force and Motion" (Discovery Education lesson 2 activity 3 ) What's the difference between speed and velocity *
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From what I understand, Speed is a scalar value, so it can't be negative. Velocity is a vector quantity, so it can be negative (when something is moving backwards).

explanation:

crosscutting concepts have application across all domains of science. as such, they are a way of linking the different domains of science. they include patterns; cause and effect; scale, proportion, and quantity; systems and system models; energy and matter; structure and function; and stability and change.