1. The document discusses different types of motion including uniformly accelerated motion in the horizontal and vertical dimensions, projectile motion in two dimensions, and free fall as an example of uniformly accelerated motion. 2. It also discusses impulse and momentum, explaining that momentum depends on mass and velocity and that changes in momentum occur when an external force acts on an object over time. 3. Finally, it discusses different types of collisions including elastic collisions where kinetic energy is conserved and inelastic collisions where kinetic energy is not conserved, as well as different forms of energy including potential and kinetic energy.

1. FORCES AND MOTION
Uniformly Accelerated Motion: Horizontal Dimension
If a body maintains a constant change in its velocity in a given time interval along a straight line,
then the body is said to have a uniform acceleration. Consider an airplane on a runway
preparing for takeoff. Positions taken at equal time intervals are indicated in the figure below
Uniformly Accelerated Motion: Vertical Dimension
So on Earth, when you throw something up, it will go down. Things thrown upward always fall at
a constant acceleration which has a magnitude of 9.8 m/s2. This means that the velocity of an
object in free fall changes by 9.8 m/s every second of fall.
Consider a stone dropped from a cliff as shown in the Figure 2. For equal time interval, the
distance travelled increases quadratically.
Free-fall is an example of uniformly acceleratedmotion, with its acceleration being -9.8 m/s^2,
negative because it is downward.
Motion in Two Dimensions
“Oh the places you’ll go! There is fun to be done! There are points to be scored. There are games to
be won. And the magical things you can do with that ball will make you the winning-est winner of
all.” - Dr. Seuss
Many neighborhood games you join and sporting events you play and officiatein MAPEH classes
involve flying objects or balls.
Have you noticed the curved paths they make inmid-air? This curve is what naturally happens
when an object, called a projectile, moves in two dimensions – having both horizontal and
vertical motion components, acted by gravity only. In physics this is called projectile motion.
Not only balls fly when in projectile motion. Have you noticed that in many sports and games,
players come “flying” too? Understanding motion in two-dimensions will help you apply the
physics of sports and enhance game events experiences.
Impulse and Momentum
What affects motion?
Consider a cargo truck with a mass of 10,000 kilograms traveling at a velocity of 40 kilometers
per hour and a small car with a mass of 2000 kilograms traveling at the same velocity as shown
below. If the two vehicles suddenly lose their breaks and crash against the brick wall, which do
you think would be more damaging? On what factor would the impact of collision depend if
their velocities are the same?
If you suggested that it would be the mass of the truck, then you are correct. Although the two
vehicles have the same velocities but different masses, the impact of the truck’s collision with
the brick wall is far damaging comparedwith the impact of the car’s collision with the brick wall.

2. What affects momentum?
Which of the two toy vehicles was more difficult to stop – the lighter one or the heavier one?
The heavier one is more difficult to stop. This is because it possesses a greater inertia in motion
which depends on an object’s mass and velocity. Do you still remember Newton’s First Law of
Motion? It is also known as the Law of Inertia. An object’s momentum is also known as inertia in
motion. For objects moving at the same velocity, a more massive object has a greater inertia in
motion therefore a greater momentum. Momentum depends on two factors, mass and velocity.
Two cars of the same mass but different velocities will also have different momenta.
What causes changes in momentum?
Changes in momentum happen every time. A fast-moving car when suddenly stopped might
have damaging effects not only to the vehicle itself but also to the person riding it. Various
devices have been installed in vehicles in order to ensure the safety of the passengers. The use
of seatbelts is even prescribed by law in order to lessen injuries from car crashes. Inflatable
airbags are also installed in most cars aimed to increase the time of impact between the driver
or passenger and the crashing vehicle in the event of an accident. Can you think of some other
safety devices installed on vehicles?
In physics, an external force acting on an object over a specific time leads to a change in
momentum of the object. A special name is given to the product of the force applied and the
time interval during which it acts: impulse.
Impulse = force x time
Remember!
Momentum is a vector quantity. It must have both magnitude (numerical value) and direction. The
direction of the momentum vector is always in the same direction as the velocity vector. Like all
vector quantities, momentum vectors can be added. For situations in which the two vectors are in
opposite directions, one vector is considered negative and the other positive.
Elastic and Inelastic Collisions
A collision is an encounter between two objects resulting in exchange of impulse and
momentum. Because the time of impact is usually small, the impulse provided by external forces
like friction during this time is negligible. If we take the colliding bodies as one system, the
momentum of the system is therefore approximately conserved.
The total momentum of the system before the collision is equal to the total momentum of the
system after the collision
total momentum before collision = total momentum after collision

3. Collisions are categorizedaccording to whether the total kinetic energy of the system changes.
Kinetic energy may be lost during collisions when (1) it is converted to heat or other forms like
binding energy, sound, light (if there is spark), etc. and (2) it is spent in producing deformation
or damage, such as when two cars collide. The two types of collision are:
1. Elastic collision – one in which the total kinetic energy of the system does not change and
colliding objects bounce off after collision.
2. Inelastic collision – one in which the total kinetic energy of the system changes (i.e.,
converted to some other form of energy). Objects that stick together after collision is said to be
perfectly inelastic.
WORK, POWER, AND ENERGY
Mechanical Energy Rules! (Of forms and transformations...)
Energy is the name of the game. Everything exists or cease to exist because of its presence or
absence. It is stored in different forms and can transfer and/or transform. It can be transferred
without being transformed. It can also be transformed without being transferred. It can also be
transformed during transfers.
In general, the energy acquired by objects upon which work is done is known as mechanical
energy. You have learned in Grade 8 Science that mechanical energy fall under two categories:
Table 1. Different Forms of Mechanical
Energy Pls. redraw
A. Potential Energy - Energy in matter due to
arrangements of its parts, its
composition, location and structure. It
is commonly considered as a stored
energy having the potential to do
mechanical work.
- The various forms of potential
energy:
gravitational chemical elastic electrical nuclear
B. Kinetic Energy - Energy in moving matter and wave.
- Some forms of kinetic energy:
motion radiant sound thermal wave
*Chemical, electrical and nuclear energies in general exhibit characteristics that are
electromagneticin nature...though they also have potential energy.

4. Table 2. Mechanical
Potential and Kinetic
Energy Equations Pls.
redraw
A. Potential Energy
𝑃𝐸𝑔𝑟𝑎𝑣 = 𝑚𝑔ℎ
𝑃𝐸𝑒𝑙𝑎𝑠 = 12 𝑘𝑥2
where
PEgrav = gravitational
potential energy
m = mass of object
g = acceleration due to
gravity
h = height or elevation
difference
where
PEelas = elastic potential
energy
k = spring constant
x = compression or
extension length
B. Kinetic Energy
𝐾𝐸 = 12 𝑚𝑣2 where
KE = kinetic energy
m = mass of object
v = velocity of object
Diagnostic Assessment(Answers)
1. A
2. F
3. D
4. D
5. D
6. B
7. D
8. A
9. B
10. C
11. C
12. A
13. B
14. A
15. C
16. B
17. A
18. A
19. C
20. A
Summative Assessment (Answers)
1. B
2. D
3. B
4. D
5. A
6. C
7. B
8. D
9. C
10. C
11. A
12. C
13. C
14. A
15. B
16. B
17. A
18. A
19. C
20. A