2.  To learn Newton’s Three Laws  Be able to provide example of the laws  Draw Free Body Diagrams correctly  Use Newton’s second law to solve for F, m, and a of a system  Apply the friction equation to solve for F f, µ or F N

3.  An object in motion stays in motion or an object at rest stays at rest unless acted upon by an outside force.  In layman’s terms, stuff will keep doing what it’s doing unless you mess with it.  Examples: ◦ A Demo… ◦ A tablecloth…tablecloth ◦ What happens if you turn your car sharply to the right? You go straight. The car moves out from under you.)

4.  F = ma  Acceleration of an object varies directly with the force applied and indirectly with the mass of the object.  Examples: ◦ Big kid and little kid on roller skates—each gets the same push ◦ Baseball—if I want the ball to go farther, what needs to happen? ◦ A demo:  2nd Law 2nd Law

5.  For every action, there is an equal and opposite reaction.  Examples: ◦ A fire extinguisher… A fire extinguisher… ◦ Canoes Canoes ◦ You sitting in your chair

6.  You push on the earth, and the earth pushes on you.  A car pushes on the road as the road pushes on the car.  This equal and opposite force upwards is called the normal force. FNFN  The normal force is why you don’t fall down when you sit in a chair.  Always directed 90° from plane of object

7.  The resulting force an object feels is a sum of all forces acting upon it.  The donkey moves as if there is one overall pull in one direction

8.  Shows the directions all the forces acting upon an object  Types of forces: ◦ Applied ◦ Gravity ◦ Normal ◦ Friction ◦ Drag—a type of friction ◦ Tension—rope holding attached to an object ◦ Spring—coming soon to a classroom near you

9.  Use a dot or box to represent your object  Draw each force as an arrow  Attach each arrow to the dot/box  Aim the tip of the arrow in the direction the force is acting

10.  What forces are acting on the “rollerskate”? Hint: they can be at an angle.  Rope (tension)  Friction  Gravity—sled’s mass plus Naomi  Normal

11.  The resultant force on an object is the sum of all forces on that object. ◦ ΣF x =ma x ◦ ΣF y =ma y  If the object is not accelerating (it can be moving) in a given direction the ΣF = 0.

12.  What condition must be met for the “rollerskate” to accelerate?

14. FNFN T mg 30° Notice F N is perpendicular to the plane.

15. FNFN T mg 30°

16. FNFN T mg 30° mgcos30 mgsin30

17.  A child holds a sled at rest on a frictionless, snow-covered hill. If the sled weighs 77.0 N, find the tension, T, exerted by the rope on the sled and the normal force exerted by the hill on the sled.

18.  Set your frame of reference.  The sled is at rest for ΣF x = 0 and ΣF y = 0.  Add up all the x direction forces. ΣF x = 0 0 = T - mgsin30 0 = T – 77(sin30) T = 38.5 N  Add up all the y direction forces. ΣF y = 0 0 = F N – mgcos30 F N = 77(cos30) F N = 66.7 N

19.  You can have an acceleration up or down the ramp.  If this happens, ΣF x = ma and ΣF y = ma for the system.  Hint: usually ΣF y = 0 because the object is not moving up and/or down on the plane of motion. (The sled is not bouncing down the hill.)

20.  The equation for friction is ◦ F f = force due to friciton ◦ µ = coefficient of friction  Two types: Static (not moving) and kinetic (moving) ◦ F N = force Normal  Friction always opposes motion!!!!!

21. FNFN T mg 30° You then rework your sum forces in the x direction to include the oppositional force of friction. FfFf

22.  Newton’s Three Laws ◦ Objects in motion (at rest) stay in motion (at rest) unless acted upon by an outside force ◦ F = ma ◦ For every action, there is an equal and opposite reaction.  ΣF x = ma and ΣF y = ma  F f = µF N

23.  A gust of wind blows an apple from a tree. As the apple falls, the force of gravity on the apple is 9.25 N downward, and the force of the wind on the apple is 1.05 N to the right. Find the magnitude and direction of the net external force on the apple.

24.  The net external force on the propeller of a 3.2 kg model airplane is 7 N forward. What is the acceleration of the plane?

25.  A 6.0 kg object undergoes an acceleration of 2 m/s 2. What is the magnitude of the net external force acting on it? If this same force is applied to a 4 kg object, what acceleration is produced?

26.  A catapult exerts 450,000 N on an airplane of 23,000 kg. It starts from rest and reacher 72 m/s at the end of 85 m. The engines are producing 300,000 N of thrust. What is the average friction on the plane during the launch?

27.  A dockworker loading crates on a ship finds that a 20-kg crate, initially at rest on a horizontal surface, requires a 75-N force to set it in motion. However, after the crate is in motion, a horizontal force of 60-N is required to keep it moving with a constant speed. Find the coefficients of static and kinetic friction between the crate and the dock.