Accelerationand

Gravity

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 -> vi = 10 m/s-> vf = 73 m/s-> t = 9.0 s

Step 2: Substitute a = vf – vi = 73m/s – 10m/s t 9.0s

Step 3: Solvea = 63m/s = 7m/s2 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 kg Weight on Earth -> 1617 NMass 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/s2

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/s2 This means that it would increase 9.8m/s2

for each second it falls…• 1 second -> 9.8m/s2

• 2 seconds -> 19.6m/s2

• 3 seconds -> 29.4m/s2

Acceleration due to gravity continued…Air resistance opposes acceleration due to gravity. The greater the surface area, the greater the air resistance that acts on it. Terminal 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