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PHYSICS 9 Reviewer 2nd Qtr
2.1 Free Falling Motion
✭ Free Fall - objects falling only because of gravitational force
- acceleration due to gravity (g) g = -9.8 𝑚/𝑠^2 ͢ not dependent on the object's mass
- all free-falling objects have the same rate of fall regardless of its mass ✭ Air Resistance - force exerted by air molecules on a moving object (goes against the object)
- also known as drag or air friction
MASS ≠ WEIGHT
- mass is a scalar quantity, while weight is a vector quantity Scalar - only has magnitude (size) Vector - has direction & magnitude Speed - how fast or slow Velocity (v) - change in speed over time Acceleration - change in velocity over time (vector) ✭ Acceleration due to gravity (-9.8m/s^2) - change in velocity over time
- Constant acceleration ✭ VACUUM - the only force acting on an object in free fall is gravity, thus it experiencesUNIFORM ACCELERATION MOTION DOWNWARD.
- all objects, regardless of their shape, size, or mass, would fall at the…. SAME RATE!!! UAM - a motion in a straight line. The body has constant acceleration ✧ Objects fall at different rates because of air resistance, not because of their mass. When air resistance is reduced, objects of different masses fall at the same rate of fall. 2 Motion Characteristics of Free Falling Objects
- Free falling objects do not encounter air resistance
- All free falling objects on earth accelerate downwards at a rate of 9.8m/s^
- Acceleration is downwards (speeds up as it falls downward) ✧ Free fall is independent to Mass
Representing Free Fall by Graphs
✭ Position vs Time Graph
- how position changes over time Absolute position over time
- curved line = accelerated motion
- Parabolic - curved graph (has acceleration)
- Slope of P/T graph = velocity ⤷ steeper = more velocity
- FF body = increasing distance traveled because of gravity
- distance- length
- displacement - change in the object's position from where it started to where it is at any moment during the fall
- the position of the ball decreases as the time increases (inverse) The longer it falls, the farther it is from where it started. ✧ Position (scalar) changes each second in the fall ✧ Distance increases each second ✧ Displacement (vector) is negative/downward (values increases in magnitude as time passes)
The object's velocity is increasing (in magnitude) and becomes more negative which means its accelerating downward Initial velocity is always 0 d = P 2 - P 1
✭ Velocity vs Time Graph
- diagonal line = accelerated motion
- m = 𝑦₂−𝑦₁ 𝑥₂−𝑥₁
- Acceleration of a FF body is constant because the increase in velocity for each time interval is constant
- Velocity line going down = negative acceleration
- Direction of acceleration = downward *both graph represent negative acceleration
Velocity:Vf = Vi +gt Displacement formula: (forgot it)
Distance:
d = 𝑉𝑖𝑡 +
2 𝑔𝑡
d =
2 − 𝑉𝑖 2 2𝑔 *Total distance:
- multiply distance covered going up 2 (d⬆ + d⬇) Time up = time down (no air resistance) (inversely proportional)
2.2 Projectile Motion
✭ Projectile Motion - the motion of an object thrown (projected) into the air when, after the initial force, launches the object.
- air resistance is negligible
- influenced by only gravity
- combination of horizontal and vertical motion (curved motion)
- continues in motion by its own inertia after being projected or dropped
- parabolic trajectory = path taken
FREE FALL VS PROJECTILE MOTION
- free fall s direction of motion is vertical direction (up and down; straight line).
- projectile motion both directions, curved path
Calculating the Displacement
*Vertical motion & horizontal motion are independent of each other
- happens at the same time (won’t affect each other)
AT MAXIMUM HEIGHT
Velocity = 0 Acceleration: -9.8 m/s^ AS IT GOES UP Velocity is decreasing Acceleration: -9.8 m/s^ AS IT GOES DOWN Velocity increases Acceleration: -9.8m/s^ CONCLUSION:
- at 45 degrees the range is the longest
- complementary angles give the same range
- at 90 degrees is the maximum height
- the greater the initial velocity, the longer the range, the higher the maximum height, the longer the time of flight.
- horizontal velocity is constant of the projectile
- vertical motion changes due to acceleration due to gravity and is a free fall motion
- time to reach the highest point multiplied by 2 = total time of flight
- complementary angles give the same range
2.3 Momentum and Impulse
- Mass and velocity affect momentum
- An object with momentum is hard to stop ✭ Momentum - mass in motion
- vector quantity (has direction)
- p = mv
- units: kg-m/s
- 0 velocity = no momentum Mass & Momentum
- directly proportional
- as mass increases, momentum also increases, vice versa
- the greater the mass, the greater force needed to stop an object. Velocity & Momentum
- directly proportional
- as velocity increases, momentum increases linearly (something increases at a constant rate, or by the same amount for each unit of time)
- they act as one system/mass as they move as one or stick together
- has zero velocity, as they collide comes at rest
- may move apart but with a loss of KE from the system The objects may stick together
- same mass/equal opposite velocity >
comes to rest
- different mass/equal opposite velocity >> move together in the direction of the object w/lesser mass -same mass/unequal opposite velocities>> will move together in the direction of the object that had higher initial velocity -different mass/unequal opposite velocity>>move together but the direction caries ✧Perfect inelastic collision is the objects stick together ✧Partial inelastic is when objects separate after collision, some KE loss, momentum conserved Total momentum after inelastic collision
CONCLUSION
- In elastic collisions, momentum and kinetic energy are conserved, allowing objects to bounce off each other without any loss of energy, leading to predictable final velocities based on their masses and initial velocities.
- In inelastic collisions, while momentum is conserved, kinetic energy is not, often resulting in a loss of energy that is transformed into other forms, such as heat and sound.
- In perfectly inelastic collisions, the colliding objects stick together, emphasizing the significance of mass and velocity in determining their combined motion.
2.4 Energy Conservation
✭ Potential energy - stored energy in an object due to its condition
PE = mgh
Kinds of potential energy:
- Gravitational
- Chemical
- Elastic ✭ Kinetic Energy - energy of motion when an object is moving
- object in motion has speed, velocity, kinetic energy and momentum
KE = 𝑚
2 𝑣
● Both rely on mass | forms of mechanical energy ● J = Joules
ENERGY IS SCALAR
- Kinetic energy is directly proportional to the square of its
speed (KE ∝ 𝑣^2 ) ✭ Total mechanical energy
- sum of PE and KE (scalar)
- constant throughout the motion (law of conservation of energy)
- not changing since energy cannot be created nor destroyed, can only be converted
- the capacity to do work
- ME = PE + KE ME System
- output of force depending on the input
- exerted force ✧Mass & PE
- directly proportional ✧Acceleration & PE
- directly proportional ✧Height & PE
- directly proportional ✧Speed & KE
- directly proportional ✧Mass & Velocity
- directly proportional
- PE is highest at point A and D because the pendulum is at its maximum height as the KE is at its lowest
- As it moves downward PE decreases, while KE increases because its speed is increasing ✧As it rises: the potential energy increases as height increases vice versa ✧As the pendulum moves downward its PE decreases, KE increases & its speed increases | at the lowest point PE is at 0J and KE is at its maximum Conservation of mechanical energ y
Total Energy
TE = mgh + 𝑚
- In an ideal mechanical system, the total mechanical energy is conserved meaning it remains constant over time. PE initial + KE initial = PE final + KE final
Formula for height:
- to travel from point A to B
- electrons move to the side with less electron pressure through conductors
- no force is pushing the electrons
Series
- same current flows through all the components in the circuit | has only one path and breaking the path anywhere stops the current from flowing
✭ OHM’S LAW
- fundamental principle in electricity that relates voltage, current, and resistance in a simple equation.
✭ RELATIONSHIPS
Voltage & Current
- directly proportional (when resistance is constant) Voltage & Resistance
- directly proportional (when current is constant) Current & Resistance
- inversely proportional (when voltage is constant) ✭ 2 types of circuits Parallel
- electric current has multiple paths to flow through
- constant voltage across all ends
By Chelsea Borja
