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Unformatted text preview: Physics 102 Describing 1D Motion Slide 1 Department of Physics, The University of Arizona Describing 1D Motion: Acceleration Motivation: Velocities are rarely constant. We must understand how to describe how they change. Objectives for this section: Learn definitions, both numerically and graphically, of average and instantaneous acceleration Use these relationships to calculate distances, times and velocities Develop equations relating displacement, velocity and time for the special case of constant acceleration Defining Acceleration An object’s acceleration is the change in its velocity per unit time. Average acceleration: Instantaneous acceleration: i f i f t t v v t v a ≡ ∆ ∆ ≡ t v a t ∆ ∆ ≡ → ∆ lim • a has a single value for the interval t i t f • a can vary with time along the route • each can be +,  or 0 ; takes the sign of ∆ v • units (m/s)/s or m/s 2 Signs of v and a : Object moving right ⇒ v > 0 and speeding up ⇒ v f > v i ⇒ a > 0 and slowing down ⇒ v f < v i ⇒ a < 0 Object moving left ⇒ v < 0 and speeding up ⇒ v f < v i ⇒ a < 0 and slowing down ⇒ v f > v i ⇒ a >0 v f more negative than v i v f less negative than v i When an object speeds up , its v and a have the same sign. Physics 102 Describing 1D Motion Slide 2 Department of Physics, The University of Arizona Physics 102 Describing 1D Motion Slide 3 Department of Physics, The University of Arizona Defining Acceleration Again notice the difference in mathematical notation: Average acceleration: Instantaneous acceleration: Whenever we say "acceleration " with no adjective, we always will A key point  a a mean "instantaneous acceleration" Sign of Acceleration Table...
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 Spring '09
 
 Acceleration, Department of Physics, Describing 1D Motion, Arizona Describing 1D, 1D Motion Slide

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