falling objects

in the vertical or y-direction,

objects move under the influence of gravitational force

without another force (such as air friction), falling objects

• all objects fall with the same acceleration near the surface of the planet

g - acceleration of all objects falling towards Earth’’s surface

• 9.8 m/s

what affects the value of g

• air friction (upward) will reduce g (downward)

• the mass of a falling object does NOT affect the value of g

  • unless noted, we will not consider air friction/air drag

innertia

• the tendency of mass to remain at rest or constant motion unless acted on by an unbalanced force

• heavier objects require greater inertia because they require more force to accelerate

  • heavier objects are more sluggish, and resist acceleration

• mass is innertia. more mass = more innertia

velocity of falling object

• start with v=0 at t=0, pick up 9.9 m/s of speed each second after that, until it hits the ground

• all objects with no external forces have the same v(t) graph

• velocity increases downward. the slope is acceleration, which is negative (downwards)

  • acceleration = 9.8 m/s/s at every point on the graph

displacement on v(t) graph

• area under graph (between line and x-axis)

• displacement downward at 3 seconds is 45 m

when is the answer negative

• if you make downward (g) negative, the change in y will be negative

why is a falling object accelerating

• because it is picking up speed as it falls downward

initial velocity of a dropped object

zero

displacement downward vs. time graph of a falling object

• the slope is negative and decreasing, so the velocity is negative and increasing in the negative direction

• each second, the ΔY gets bigger

• the grapg is a curve because the object is accelerating

instantaneous velocity of displacement downward vs time graph

• the slope at each point

• the slope increases in the negative direction - the object speeds up as it fals

object being thrown up

• the acceleration vector is downward the ENTIRE TIME (way up & down)

object being thrown up (on way up)

• speed decreases

  • because the velocity vector is upward, and the acceleration vector is downward

  • objects speed will decreaseuntil it reaches zero, then it will trun around and fall downward

vertical speed of ubject at max height of throw

• zero

object being thrown up (on the way up)

• speed increases downward

  • because the velocity vector is downward, and the acceleration vector is also downward

v(t) graph of an object thrown upward

• constant velocity; crosses zero

• the slope is the same the entire time (so acceleration is -9.8m/s/s the ENTIRE TIME)

postition-time graph of ball being thrown

• NOT the path of the ball, just the height of throw for ecah second.

• top of motion is 2 ish seconds

if you throw a ball straight upward, when is its velocity zero?

at the peak of its motion; its max height

if you drop a ball, when is its velocity zero

• at the moment it is dropped

• the INITIAL velocity

• also after it has hit the ground and come to a stop

if you throw a ball or drop a ball, when is acceleration the greatest

• the acceleration s a constant -9.8 m/s/s if there is no air drag; no max acceleration, it is always the same

if you drop a bowling ball and basketball at the same time, which one will hit the grown first

• in the absence of air friction, all obects will hit at the same time.