G RADE 9 MYP S CIENCE – P HYSICS Energy, Forces & Motion

S TATEMENT OF INQUIRY We can use energy to change the form or movement of an object

K EY & R ELATED C ONCEPTS Change Form, Energy, Movement, Interaction

G LOBAL C ONTEXT Scientific & Technical Innovation

K INEMATICS Kinematics is the study of how objects move

U NIFORM M OTION Uniform Motion is motion in which the velocity remains constant. Distance is defined as how far an object has moved. Speed is defined as the magnitude of velocity. Velocity is defined as the rate of change in an object’s position.

S CALAR Q UANTITIES A scalar quantity is a quantity that has a magnitude (size) only. Examples are distance (5 km), time (8 h), energy (25 J), speed (45.0 m/s), mass (12 kg), temperature ( 25ºC) and sound 145 (dB)

V ECTOR Q UANTITIES A vector quantity is a quantity that has both a magnitude and a direction. Examples are displacement (65.0 km, West) velocity (15.0 m/s, East) force (50 N, down) acceleration (2.5 m/s 2, North)

VELOCITY FORMULA v = velocity (speed) m/s, km/h d = distance km, m t = time s, h

A CCELERATED M OTION In uniformly accelerated motion, the acceleration is constant; it does not change. Acceleration is the rate of change in the velocity. Units: ms -2 The symbol for acceleration is “a” Acceleration is a vector quantity

A CCELERATED M OTION a = acceleration ms -2 v = velocity (speed) ms -1, km/h t = time s, h

A CCELERATED M OTION If the acceleration is positive, the object is speeding up. If the acceleration is negative (deceleration), the object is slowing down. You must write the negative sign into your calculations.

G RAPHING M OTION

M OTION G RAPHS There are three graphs possible for motion. Displacement (Distance) vs Time Velocity (Speed) vs Time Acceleration vs Time

P OSITION – T IME GRAPH

P OSITION VS T IME G RAPH The slope of a Position vs Time graph is equal to the Velocity of the object. m = y 2 – y 1 = Velocity x 2 – x 1

E XAMPLE Find the speed at 5 seconds!

E XAMPLE Using the given graph find the velocity of the object in intervals (1s – 3s) and (3s – 5s).

V ELOCITY (S PEED ) VS T IME G RAPH - S LOPE The slope of a velocity vs time graph is equal to the acceleration of an object. m = y 2 – y 1 = acceleration x 2 – x 1

E XAMPLE Find the acceleration for each interval in the velocity-time graph (0-4, 4-8, 8-12, 12-16, 16-20, 20-24, 24-30)

V ELOCITY (S PEED ) VS T IME G RAPH - A REA The area under a velocity vs time graph is equal to the position (distance travelled) by the object.

R EVIEW The SLOPE of a Position Time graph is equal to the VELOCITY of the object. The SLOPE of a Velocity Time graph is equal to the ACCELERATION of the object. The AREA under a Velocity Time graph is equal to the DISTANCE travelled by the object.

R EVIEW If a graph is given, you must use either the slope or area (depending upon the question) to solve the graph. Do not use formulas to solve graphs.

F REELY F ALLING O BJECTS

G ALILEO Galileo discovered that objects accelerate uniformly at the same rate as they fall. According to Galileo if the air resistance of an object is great enough, the object will stop accelerating and will fall at a constant speed.

A CCELERATION DUE TO G RAVITY C ONSTANT The symbol is g It has a value of – 9.81 m/s 2 near the surface of Earth. As we move away from the surface, the value of g decreases. Acceleration due to gravity is a vector and the direction is always down, toward the centre of the Earth.

T ERMINAL V ELOCITY An object falling through the atmosphere eventually reaches a velocity where the air resistance is great enough to prevent further acceleration. This is called terminal velocity.