Newton’s Laws

1. Newton’s Laws

2. Targeted Skills for Newton’s Laws (Lecture ONLY) 1.Identify and apply Newton’s Laws of Motion to a variety of qualitative and quantitative problems. 2.Identify: Gravitational Forces (Fg), Tension Forces (FT) Normal Forces (FN) and Frictional Forces (Ff). 3.Draw free body diagrams (FBD). 4.Analyze position versus time, velocity versus time and acceleration versus time graphs for regions of zero and non-zero net force. 5.Solve dynamics problems.

3. Newton’s First Law of Motion Describe the motion of an arbitrary object setting in the room. Define Mass/Inertia Inertia – A measure of a bodies resistance to a change in motion. Mass = Inertia Mass – A measure of a bodies resistance to a change in motion

4. Newton’s First Law of Motion Describe the motion of an arbitrary object sitting in the room. What is required to change an object’s motion? An UNBALANCED Force Define Newton’s First Law of Motion (Also known as Law of Inertia) An object will remain in a state of constant motion unless acted upon by an unbalanced force.

5. Newton’s Second Law of Motion What is required to change an object’s motion? An UNBALANCED Force UNBALANCED Force = NET Force NET Force = F (Sum of forces) What results if an unbalanced force is applied to an object? ACCELERATION Define Newton’s Second Law of Motion The acceleration of an object is proportional to the net force applied to the object and inversely proportional to the object’s mass.

6. Newton’s Second Law of Motion Equation of Newton’s Second Law of Motion F = ma Questions How do we know if we have an unbalanced force? If there is an unbalanced force, in what direction is it acting? Answer FREE-BODY DIAGRAM A diagram of the object involved in a problem and the forces exerted on the object.

7. Free-Body Diagram Construction Horizontal / Vertical Scenarios A jet plane is gliding at a constant elevation at a constant velocity. Draw the Free-Body Diagram of the forces acting on the plane. NO air resistance. A jet plane is flying at a constant elevation at a constant velocity. Draw the Free-Body Diagram of the forces acting on the plane. ConsiderAir Resistance.

8. Free Body Diagram Construction Horizontal / Vertical Scenarios A jet plane is flying at a constant elevation with an increasing velocity. Draw the Free-Body Diagram of the forces acting on the plane. Consider Air Resistance. A jet plane is flying at a constant elevation with a decreasing velocity. Draw the Free-Body Diagram of the forces acting on the plane. Consider Air Resistance.

9. Free Body Diagram Construction • Rules • Draw an arrow representing the weight of the object. • Label the arrow Fg. • 3. Draw additional arrows in the appropriate directions to represent any forces acting on the object. The length of the arrows should be proportional to the quantity of the force.

10. Free Body Diagram Construction • Rules • Label arrows with appropriate names, e.g.: • Force of Gravity, Fg • Tension, FT • Normal, FN • Friction, Ff • Remember, ONLY the arrows constitute the free body diagram.

11. Free Body Diagram Worksheet

12. Example Problem 1 F2 F1 10 kg Two forces are applied to a 10 kg block. Calculate the net force block on the block if F1 equals 15 N and F2 equals 30 N. F = 30N –15 N F = 15 N to right What is the block’s acceleration? F = ma

13. Example Problem 1 F2 F1 10 kg Two forces are applied to a 10 kg block. Calculate the net force block on the block if F1 equals 15 N and F2 equals 30 N. F = 15 N to right What is the block’s speed after 4 seconds if it was initially at rest? F = 15 N to right G: U: vf= ________ E: F=ma S: S:

14. Example Problem 2 Fred and Wilma push a stalled car at constant velocity along level ground. If Fred and Wilma push to the right with 395 N and 275 N respectively, what is the magnitude of the opposing force? Identify the opposing force. F = 395N + 275 N + f = 0 N Identify the opposing force. constant velocity--acceleration = 0 G: U: Ff = ______ E: F=ma S: S:

15. Example #3 A dirt buggy has a mass of 575 kg. The buggy uniformly accelerates from rest for 4 seconds and travels 35 meters. What’s the buggy’s acceleration? G: m = 575 kg vi = 0 t = 4 s d = 35 m U: acceleration E: d = vit + ½at2 S: See Overhead S: See Overhead

16. Example #3 A dirt buggy has a mass of 575 kg. The buggy uniform accelerates from rest for 4 seconds and travels 35 meters. How fast is the buggy traveling after accelerating for 4 seconds?  G: m = 575 kg vi = 0 t = 4 s d= 35 m U: velocity E: vi = vf + at or vf2 = vi2 + 2ad S: See Overhead S: See Overhead

17. Example #3 A dirt buggy has a mass of 575 kg. The buggy uniform accelerates from rest for 4 seconds and travels 35 meters. What net force is applied to the buggy? G: m = 575 kg vo = 0 t = 4 s d = 35 m U: net force E: SF = ma S:See Overhead S: See Overhead

18. Example #4 The maximum force a grocery sack can withstand and not rip is 250N. If 20 kg of groceries are lifted from the floor to the table with an acceleration of 5 m/s, will the sack hold? if F1 equals 15 N and F2 equals 30 N. G: m = 20 kg a = 5 m/s2 Fmax = 250 N F2= 30 N U:F=______ E:SF = ma + mg S: See Overhead S: See Overhead

19. Newton’s Third Law Definition of Newton’s Third Law of Motion When two bodies interact, the forces on the bodies from each other are always equal in magnitude and opposite in direction. These are referred to as Action-Reaction pairs of forces. Horse-Cart Problem Draw ALL the forces acting on the horse, cart and roadway.

20. Newton’s Third Law Identify action-reaction pairs of forces. Explain how the horse can move.

21. Newton’s Third Law Explain how the horse-cart can move. Behavior of Forces Internal Forces – Come in pairs (action-reaction), cancel one another, and can NOT accelerate an object. External (applied) Force – Individual forces which may accelerate an object (SF > 0). All type of forces (Fg, FN, FT, Ff) can behave as internal and external forces.