Ch. 13-1 Notes Part 2

Riddle me this….. Imagine that two birds leave the same tree at the same time. They both fly at 10km/h for 5 min, 12 km/h for 8 min, and 5km/h for 10 min. Why didn’t they end up at the same place?

Direction matters…. The birds went in different directions!!! Their speeds were the same, but they had different velocities.

Velocity: Direction Matters!! 9.) The speed of an object in a particular direction is called velocity. 10.) BE CAREFUL! Do not confuse speed & velocity; they do not mean the same thing! So, what is the difference between speed and velocity? 11.) Velocity MUST include the “direction” that the object is moving!

Example of Speed vs. Velocity Speed: A car traveling 60 mph Velocity: A car traveling 60 mph east Direction is added to the object’s velocity. EX: When you use a compass to determine the direction in which you are walking 5 mph.

How do these thrill rides show velocity? They are changing direction and/or speed.

Acceleration 12.) The rate at which velocity changes over time is called acceleration. 13.) An object accelerates if its speed, direction, or both change.

Did acceleration occur? Scenario 1:You are riding your bike at 9km/h. Ten minutes later, your speed is 6km/h. (Yes!! Acceleration occurred because speed decreased) Scenario 2:You ride your bike around the block at a constant speed of 11km/h. (Yes!! Acceleration occurred because direction changed) Scenario 3:You ride your bike in a straight line at a constant speed of 10km/h. No!! Acceleration did not occur because neither speed nor direction changed.)

Are you accelerating if… 1. You pick up the pace walking? 2. A car turns on a race track? 3. You slow down to a steady walk? 4. An object is moving in a circle? What about you standing still? Yes! Yes! Yes! Yes! Yes! Your are traveling in a circle as the earth rotates!

Acceleration? Yes…direction is changing

Force – push or pull 14.) a force is a push or a pull and always acts in a certain direction. Force is measured in newtons(N) Ex. If you push something, the force is in the direction of the push. 15.) A force can change the acceleration of an object. This acceleration can be a change in the speed or direction of the object.

Mass vs. Weight 16.) Mass is the amount of matter in an object, so will it ever change? 17.) Mass is measured with a balance scale 18.) Weight, however, is the measure of the amount of gravitational force exerted on an object. Weight is measured with a spring scale

Mass vs. Weight 19.) The Si unit of weight is Newtons. 20.) Weight Is not the same as mass! - 21.) Mass is measured in grams/kilograms. Even if the mass of an object doesn’t change its weight will change if its distance from Earth changes.

Mass versus Weight Mass is….. A measure of the amount of matter in an object. Always constant for an object no matter where the object is in the universe. Measured using a balance scale in grams (G) Weight is….. A measure of the gravitational force on an object. Varies depending on where the object is in relation to the Earth Measured using a spring scale in Newtons (N) Same chart as page 185 in your book

Something to think about… Does this astronaut have the same mass on Earth as he does on the moon? Does he have the same weight? Yes, same mass…….No, different weight, because there is no gravity/ farther away from earth so the gravitational force decreases