Acceleration The rate at which velocity changes. Includes: increasing speed decreasing speed changing direction (with no change in velocity)

final velocity – initial velocity time acceleration = *If answer is positive -> speeding up *If answer is negative -> slowing down *Units are m/s or m/s² s How do you find the acceleration?

Sample problem 1: A car traveling east accelerates from 10m/s to 73m/s in 9.0 seconds. Calculate its acceleration. Step 1: list the variables -> v i = 10 m/s -> v f = 73 m/s -> t = 9.0 s Step 2: Substitute a = v f – v i = 73m/s – 10m/s t 9.0s Step 3: Solve a = 63m/s = 7m/s 2 9.0s

Gravity force that pulls objects toward each other Law of Universal Gravitation – the force of gravity acts between all objects in the universe. Mass and distance affect the gravitational attraction between two objects.

Mass and Weight  Mass – a measure of the amount of matter in an object  measured in grams, kilograms, pounds, etc.  mass of an object does not change  Weight – the force of gravity on a person or object at the surface of a planet.  measured in Newtons (N)  weight of an object can change  weight = mass x gravity An astronaut in a spacesuit… Mass on Earth -> 165 kgWeight on Earth -> 1617 N Mass on the moon -> 165 kg Weight on the moon -> 270 N

Sample problem 2: If a person has a mass of 132pounds, what is their weight? Step 1: Convert to metric units if needed. 2.2 lbs = 1 kg 132lbs ÷ 2.2 lbs/kg = 60kg Step 2: Substitute W = m x g W = 60kg x 9.8 m/s 2 Step 3: Solve W = 588 N

Acceleration Due to Gravity  When gravity is the main force acting on an object, the object will accelerate.  On Earth, the acceleration due to gravity is 9.8 m/s 2  This means that it would increase 9.8m/s 2 for each second it falls… 1 second -> 9.8m/s 2 2 seconds -> 19.6m/s 2 3 seconds -> 29.4m/s 2

Acceleration due to gravity continued… AAir resistance opposes acceleration due to gravity.  The greater the surface area, the greater the air resistance that acts on it. erminal velocity - velocity at which the force of air resistance equals the weight of the object. (Forces are balanced, so no acceleration, but velocity remains constant.)  In the absence of air, all things will truly fall with the same acceleration. Feather and hammer on the moon