1. A review of Newton’s Third law and VECTORS! Oohhhh….ahhhhh….

2. What is Newton’s Third Law? For every action, there is always an equal and opposite reaction. For every action, there is always an equal and opposite reaction. Two forces involved – Two forces involved –ActionReaction It doesn’t matter which is which. It doesn’t matter which is which.

3. Forces Neither one exists without the other. Neither one exists without the other. Equal in strength and opposite in direction Equal in strength and opposite in direction Forces always exist in _____. Forces always exist in _____. ooops…I mean pairs. There are countless examples where we see this… There are countless examples where we see this… pears

4. Example One – Gravity and Tides When we say gravity – what is pulling on what? When we say gravity – what is pulling on what? Think of the moon and the earth…what is pulling on what? Think of the moon and the earth…what is pulling on what? The Earth pulls on the moon…the moon pulls on the earth. The Earth pulls on the moon…the moon pulls on the earth. The moon can’t pull the earth, The moon can’t pull the earth, but it can pull on something.

5. Example 2 – Rocket Engines Rocket pushes fuel exhaust out at a very fast speed…so what has to happen? Rocket pushes fuel exhaust out at a very fast speed…so what has to happen? The exhaust pushes on the rocket. The exhaust pushes on the rocket. Action: Rocket pushes fuel Action: Rocket pushes fuel Reaction: Fuel pushes rocket Reaction: Fuel pushes rocket

6. Systems Why don’t the forces cancel themselves out to zero? Because there are systems. Why don’t the forces cancel themselves out to zero? Because there are systems. A force from OUTSIDE a system is needed for acceleration. A force from OUTSIDE a system is needed for acceleration. A force from INSIDE the system plays no role in acceleration. A force from INSIDE the system plays no role in acceleration. It is a bit confusing. It is a bit confusing. Think of a car…if you want to push it, Think of a car…if you want to push it, what do you have to do? Get out and push smurf.

7. Systems - Continued The smurf couldn’t stay IN the car to push it, he had to get OUT of the car in order to apply a force and accelerate the system. The smurf couldn’t stay IN the car to push it, he had to get OUT of the car in order to apply a force and accelerate the system. Let’s use Pooh as another example. Is there acceleration… Let’s use Pooh as another example. Is there acceleration… if it’s only the wagon? if it’s only the wagon? if it’s only Pooh? if it’s only Pooh? if it’s both? if it’s both?

8. Velocity, Force, and Acceleration Velocity, force, and acceleration require two things to be complete: Velocity, force, and acceleration require two things to be complete: Magnitude (size) Magnitude (size) Direction Direction These quantities are fittingly called vector quantities. These quantities are fittingly called vector quantities.

9. Mass, Volume, and Speed These are all measurements of magnitude (size), but not _______. These are all measurements of magnitude (size), but not _______. They are all scalar quantities. They are all scalar quantities. direction size direction +

10. Vector, oh Vector Pictures are often better than words – so we use vectors. Pictures are often better than words – so we use vectors. Once again…a vector is a representation of any vector quantity (velocity, force, acceleration) by an arrow. Once again…a vector is a representation of any vector quantity (velocity, force, acceleration) by an arrow. It shows direction (which way) It shows direction (which way) It shows magnitude (how much) It shows magnitude (how much)

11. Vectors are used when adding and subtracting velocities Vectors are used when adding and subtracting velocities If the vectors are in line it’s easy… If the vectors are in line it’s easy… 5 N10 N+=15 N 5 N-10 N=5 N

12. Resultants If the vectors are not in line, it gets slightly tricky. To make things simple, we use the parallelogram rule. If the vectors are not in line, it gets slightly tricky. To make things simple, we use the parallelogram rule. Bring the tails of two vectors together so they form a point. Bring the tails of two vectors together so they form a point. Draw lines parallel and of equal length to the vectors. Draw lines parallel and of equal length to the vectors. From the origin, draw a diagonal line – this is the resultant, or result of the two forces coming together. It’s motion in two dimensions baby! From the origin, draw a diagonal line – this is the resultant, or result of the two forces coming together. It’s motion in two dimensions baby!

13. Example… Forces: Forces: Connect the tails Parallelogram: Parallelogram: Same size and angle Diagonal = Resultant Diagonal = Resultant

14. Example 2… Which way will he go? Which way will he go? Plane Speed Wind Speed Plane’s Direction + Speed