3 Acceleration and Free Fall Acceleration The changing of an objects velocity over time Average Acceleration SI Unit ms 2 Vector Quantity Acceleration When velocity and acceleration are in the same direction the speed of the object increases with time ID: 289968
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Slide1
Chapter 3
Acceleration and Free FallSlide2
Acceleration
The changing of an object’s velocity over time.
Average Acceleration
SI Unit: m/s2Vector Quantity
Slide3
Acceleration
When velocity and acceleration are in the same direction, the speed of the object increases with time.
When velocity and acceleration are in opposite directions, the speed of the object decreases with time.Slide4
Acceleration
The camel is not slowing down, it’s velocity is increasing in the negative-
x
direction.
4.0s
v
f
=-10.0m/s
v
i
=-2.0m/sSlide5
Acceleration
The camel is slowing down, it’s velocity and acceleration are in opposite directions.
4.0s
v
i
=-10.0m/s
v
f
=-2.0m/sSlide6
Deceleration vs.
Negative Acceleration
Deceleration – Reduction in speed
Negative Acceleration – Acceleration vector is in the negative-x directionSlide7
Instantaneous Acceleration
The limit of the average acceleration as the time interval ∆
t
approaches zero. Slide8
Motion DiagramsSlide9
One-Dimensional Motion with constant acceleration
Many applications of mechanics involve objects moving with constant acceleration
Constant Acceleration
Instantaneous acceleration = average accelerationSlide10
Comparing Motion graphsSlide11
velocity as a function of time
where:
Slide12
Reality Check
A sports car moving at constant speed travels 110m
in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is its acceleration in Express the answer in terms of “
g’s,” where The initial velocity of the car is the average speed of the car before it accelerates.
The final speed is
0
and the time to stop is 4.0 s.
Slide13
displacement as a
function of time
The area under the line on a velocity vs. time graph is equal to the displacement of the object.Slide14
An automobile manufacturer claims that its super-deluxe sports car will accelerate uniformly from rest to a speed of
38.9m/s
in 8.00s
.a. Determine the acceleration of the car.
b. Find the displacement of the car in the first 8.00s
.
Slide15
velocity as a function of displacement
Slide16
Equations for motion in a straight line under constant acceleration
Equation
Information Given
by EquationVelocity as a function of time
Displacement as a function of time
Velocity as a function of displacement
Equation
Information Given
by Equation
Velocity as a function of time
Displacement as a function of time
Velocity as a function of displacementSlide17
In coming to a stop, a car leaves skid marks 92.0m
long on the highway. Assuming a deceleration of
7.00m/s
2, estimate the speed of the car just before braking.
Slide18
Free fall
When air resistance is ignored, all objects in free fall near the Earth’s surface fall at the same constant acceleration.
Galileo
Dropped objects of different weights of Leaning Tower of PisaOr did he?Inclined PlanesDiluting GravitySlide19Slide20
Free Fall
Any object moving under the influence of gravity alone
Does not need to start from rest
An object thrown up into the air is in free fall even when its altitude is increasing.Free Fall Acceleration (g)Varies slightly with latitudeDecreases as altitude increases“Up” =positive direction
Slide21
Free fall
A tennis player on serve tosses a ball straight up. While the ball is in free fall , does the acceleration
A. Increase
B. DecreaseC. Increase then DecreaseD. Decrease then IncreaseE. Remain ConstantSlide22
Free fall
A tennis player on serve tosses a ball straight up. While the ball is in free fall , does the acceleration
A. Increase
B. DecreaseC. Increase then DecreaseD. Decrease then IncreaseE. Remain ConstantSlide23
Free Fall
As the tennis ball in the previous question travels through the air, its speed
A. Increases
B. DecreasesC. Decreases then IncreasesD. Increases then DecreasesE. Remains the SameSlide24
Free Fall
As the tennis ball in the previous question travels through the air, its speed
A. Increases
B. DecreasesC. Decreases then IncreasesD. Increases then DecreasesE. Remains the SameSlide25
A baseball is hit nearly straight up into the air with a speed of 22m/s.
a.
How high does it go
?
where,
b.
How long is it in the air
?