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2*3 Newton’s 2nd Law: Push or Pull
 WDYS? (p157)
1. Person #1 =
2. Person #2 =
3. Person #3 =
 WDYT?
1. Force is _____.
2. The same force on a tennis ball will be (the same/
different) on a bowling ball because _____.
2*3 Investigate (p157)
I will use a flexible ruler to continuously push
a car across a table or floor.
1. Small Bend = _____ Large Bend = _____
2a. Push car with a small force…the car continually
_____ its speed as the force is applied.
3a. Push car with a large force…the car continually
_____ its speed as the force is applied.
2*3 Investigate (p157)
3b. Smaller bend = _____ acceleration
Larger bend = _____ acceleration
3c. Acceleration was _____ with a larger bend
3d. The greater the bend (force) pushing the object,
the _____ the acceleration
2*3 Investigate (p157)
Now use a SMALLER mass
4a. With a LARGE bend (force ) by the ruler, the
smaller object will experience a __________
acceleration than when using the previous car.
Now use a LARGER mass
5a. With a LARGE bend (force) by the ruler, the
larger object will experience a __________
acceleration than when using the previous car.
2*3 Investigate (p157)
5b. When equal amounts of a constant force are
used to push objects having different masses, the
more massive object will have _____ acceleration.
6a. If you push a larger object with a small force,
then the acceleration would be _____.
6b. If you push a smaller object with a large force,
then the acceleration would be _____.
Physics Talk (p160-167)
1. Newton’s 2nd Law of Motion
 You observed:
1. a constant force produces an acceleration (direct)
2. acceleration decreases with an increase in mass (indirect)
 Newton’s 2nd Law of Motion  a is directly
proportional to F and indirectly related to m, and
the direction of a is the same as F
 Newton (N)  is the SI unit for Force; it is equal to
(kg * m/s/s)
Physics Talk (p160-167)
acceleration = Force / mass
a=F/m
F=m×a
m=F/a
Units for acceleration (a) = m/s/s
km/h/h
Force (F) = Newton (N)
mass (m) = g
kg
Physics Talk (p160-167)
 As the result of a serve, a tennis ball (m=.058kg)
accelerates at 430m/s/s for the very brief time in
contact with the racket.
a) What is the force?
b) Could an identical force accelerate a 5kg bowling
ball at the same rate?
Physics Talk (p160-167)
1. A tennis racket hits a sand-filled tennis ball (m=275g) with a
force of 40N, what is the acceleration?
2. A weightlifter raises a 440kg barbell with an acceleration of
2m/s/s, how much force does the weightlifter exert on the
barbell?
3. Iceman creates an ice all and throws it with an acceleration
of 28m/s/s. The force of the ice ball hitting Magneto is
115N, what is its mass?
2*3 TOTD
1. The Newton (N) is = _______________.
2. If there is a large Force on a LARGE massive object, then
the acceleration will be __________.
3. If there is a large Force on a SMALL massive object, then
the acceleration will be __________.
4. What is the acceleration of a 0.6kg volleyball when a
player uses a 84N force to spike the ball?
5. What force would be needed to accelerate a 0.08kg
golf ball at 40m/s/s?
Physics Talk (p160-167)
2. Gravity, Mass, Weight, and Newton’s 2nd Law
 Newton’s 2nd Law  if there is an acceleration, then
there is an unbalanced force acting on the object
 In 2*2 Investigate, the bending ruler was due to the
force of gravity  9.8m/s/s
 Weight  is the force of gravity acting on an object,
where the equation is w = m × g
Physics Talk (p160-167)
3. Balanced and Unbalanced Forces
 The direction AND magnitude of the forces determine the
motion of the object:
a) Both forces in SAME direction = ADD
b) Forces are in OPPOSITE direction = SUBTRACT
 Free-Body Diagram  used to show the size and
direction of ALL forces acting on an object
Checking Up (p167)
1. Newton’s 2nd Law of Motion states ___.
2. For a constant force, increasing the mass of
an object will __________ its acceleration.
3. The statement means that there will be a
_______________ acting downward on the
mass due to force of Earth’s __________.
4. Your weight would __________ while your
mass would __________.
PTG (171-173)
Force (N)
mass (kg)
acceleration (m/s/s)
?
70kg
5m/s/s
800N
?
10m/s/s
70N
7kg
?
400N
?
5m/s/s
-1500N
100kg
?
?
100kg
-30m/s/s
PTG (171-173)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
On previous slide or on page 171
do not do
a=
F=
do not do
F=
a) Weight = lbs * 4.38N/lbs =
b) m=
do not do
No, the force of your hand stops acting on the ball the
moment the two are _____.
Draw a free-body diagram with forces labeled
Draw a free-body diagram with forces labeled
a=
2*3 TOTD 2