Physics 115
“Physics for FUTURE LEADERS”
Prof. Paul Steinhardt
Princeton in the Nation’s Service
Woodrow Wilson, 1896
TAKEOUTYOURWORKSHEETANDYOU’REA-B-C-DCard
(borrowandA-B-C-Dcardfromaneighborifyoudon’thaveyourstoday)
Where is the velocity zero?
Where is the acceleration zero?
Where is the force zero?
!
Fgravity = mapple g
!
| g | ~ 10 m/s2
mapple (kg) × g (m / s 2 ) = F (newtons)
“Constant” vertical force: Near Earth Gravity
Where is the velocity zero?
Where is the acceleration zero?
Where is the force zero?
Where is the velocity zero?
Where is the acceleration zero?
Where is the force zero?
!
Fgravity = mapple g
Question:
Is there a net force on the apple as it falls?
How do you know?
!
Fgravity = mapple g
Question:
if the entire Earth exerts this force on the apple,
does the apple exert a force on the Earth?
!
!
Fgravity = mapple g = mapple a
Question:
What is the acceleration?
! !
g=a
!
!
Fgravity = mapple g = mapple a
! !
g=a
Gravity Quiz (6 questions)
True or false:
Two objects with different mass released from
same height fall with the same acceleration
!
!
Fgravity = mapple g = mapple a
! !
g=a
True or false:
Two objects with different mass released from
same height fall with the same velocity.
NASA Space Power Facility (near Cleveland)
NASA Space Power Facility (near Cleveland)
!
!
Fgravity = mapple g = mapple a
! !
g=a
True or false:
Two objects with different mass released from
same height with different speeds fall with the same acceleration.
!
!
Fgravity = mapple g = mapple a
! !
g=a
True or false:
Two objects with different mass released from
same height with different speeds fall with the same velocity.
!
!
Fgravity = mapple g = mapple a
! !
g=a
True or false:
Two objects with different mass released from
same height fall with the same force.
!
!
Fgravity = mapple g = mapple a
! !
g=a
True or false:
Two objects with different masses thrown from different
heights with different velocities have the same acceleration
Newton’s 2nd Law
VECTOR EQUATION: 3 Equations in 1
!
F
FORCE
=
!
!
Δv
ma=m
Δt
CHANGE FROM
UNIFORM MOTION
Mass = resistance to change
COMPONENTS OF MOTION
PHY 115
Through these demonstrations, we aim to practice:
•
using experiments to refine our understanding of motion.
•
using graphs to interpret and describe quantitative relationships and rates of change.
•
applying physical laws to make predictions.
Demonstration:
One ball is dropped, and another ball is shot horizontally. Draw a realistic motion diagram for each ball
(that is, draw a dot for the position of each ball at several, short, equal and equally-spaced time intervals).
The initial position for each ball is shown. The bottom of the graph represents the floor. The two graphs
are supposed to be on the same scale your realistic motion should properly compare the vertical and
horizontal position of the two balls at each time interval. Briefly explain your reasoning for why you
drew each diagram as you did.
Dropped Ball:
Shot Ball:
Two archers fire arrows at the same time from
the same place at two different targets as shown
below. The magnitudes of the velocities of the
arrows are the same, but the arrows are fired
at different angles. Which arrow hits first?
A.
B.
C.
D.
A
the arrow fired at A
the arrow fired at B
both hit at the same time
need more information
B
Two arrows are launched vertically. The second
arrow has twice the velocity of the first. Which
arrow hits the ground first?
A. the first arrow
B. the second arrow
C. the two arrows hit the ground
at the same time
D. need more information
An arrow is launched with a velocity of 30 m/s
at an angle of 30°. A second arrow is launched
with a velocity of 30 m/s at an angle of 60°.
Which arrow has the higher vertical velocity?
A. the first arrow
B. the second arrow
C. the two arrows have the same
vertical velocity
D. more information is needed
An arrow is launched with a velocity of 30 m/s
at an angle of 30°. A second arrow is launched
with a velocity of 30 m/s at an angle of 60°.
Which arrow hits the ground first?
A. the first arrow
B. the second arrow
C. the two arrows hit the ground
at the same time
D. more information is needed
The velocity vectors for three arrows are
shown below. Which arrow has the highest
vertical velocity?
A
B
C
D. all three have the same vertical velocity
The velocity vectors for three arrows are
shown below. Which arrow will stay in
the air the longest?
A
B
C
D. all three hit the ground at the same time
Two archers fire arrows at the same time from
the same place at two different targets as shown
below. The magnitudes of the velocities of the
arrows are the same, but the arrows are fired
at different angles. Which arrow hits first?
A.
B.
C.
D.
A
the arrow fired at A
the arrow fired at B
both hit at the same time
need more information
B