332 - Unit 2 1D Vectors & Newton’s Laws of Motion.

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Presentation transcript:

332 - Unit 2 1D Vectors & Newton’s Laws of Motion

A. Vectors and Scalars

B. Addition of Vectors & RESULTANT In one dimension, simple addition and subtraction is all that is needed. RESULTANT VECTOR

Aristotle vs Galileo 2000 yrs of Greek influence on motion What enables an object to move? Galileo…What enables an object to continue moving? Reason out ‘resistance’ or ‘friction’

C. FORCES NET FORCE

D. TYPES OF FORCES

1) Force of Gravity (Weight) - Without gravity, how can we distinguish between a 1kg and a 2kg mass?

An astronaut’s weight on Earth is 950N. He lands on Mars and stands on a scale where it reads 359N. A) Determine the acceleration due to gravity on Mars. B) He drops a rock from a height of 1.8m. Calculate the time it takes to fall to ground below.

*Since gold is sold by weight, should you buy it in Philadelphia, Pa or Denver, Colorado? *If you want to fit into a smaller size prom dress…should you zip up in the Poconos or here in Philly?

2) Normal Force (Support Force) If the box weighed less, what would happen to the normal force acting on the box?

3) Tension Force - A force that exists within ropes, cables, wires, string, etc

4) Friction Force

E. NEWTON’S LAWS

Newton’s 1 st Law (law of inertia)

MASS

Why do all objects fall at the same rate? (|a|=g=9.8m/s 2 ) Aristotle felt heavy fell faster than light Without air resistance, a light object falls the same as a heavy object… Explain.

Newton’s 3 rd Law

A/R pairs You punch wall… You pull a rope… You press against floor…

Locomotion… Describe the action/reaction process in order to walk forward. Describe the action/reaction process in order to swim forward?

Use 3 rd law to describe the motion of: A Rocket taking off A helicopter hovering over the ground

Bug vs Bus A loaded school bus hits a bug. Which body receives the greater force of impact, bug or bus?

Who pulls harder on the rope? What determines who wins the tug of war?

Fan for boat with no wind?

Newton’s 2 nd Law -What does F net mean? -If F net = 0, what implications does that have on object’s motion?

Force Body Diagrams FBD’s Drawing forces on object helps to solve problem. If you can draw FBD, you can setup equation. Specific forces are: –Tension (F T ) –Normal (F N ) –Gravity (F g ) –Friction (F f )

2 nd Law with force diagrams A 5.0kg box is pulled to the right by a rope parallel to surface. The tension is 30N. If the box accelerates from rest to 3.6m/s in 2.0s, determine the frictional force between the box and surface.

A 900kg elevator accelerates upward at 3.0m/s 2. Determine the tension in the cable that supports the elevator.

A 17kg shopping cart is pushed down an aisle where there is a friction force of 12N on the cart. If the cart accelerates from 0.75m/s to 1.2m/s over 3.7m, determine force applied to the cart.

A) Draw FBD B) Calculate the acceleration of the krimpet C) Calculate the force of air friction on krimpet. D) Will it take the same time to fall as it did on way up? JUSTIFY. A 0.75kg krimpet is launched straight upwards with a speed of 16m/s. It takes 1.1s to reach its apex. Air friction is present.

Air Resistance during a fall

What force(s) act on an 833N skydiver at instant he steps off helicopter if it is hovering? What happens to speed of skydiver after t = 0? Therefore, what happens to force of air friction as skydiver continues to fall?

Terminal Speed When force of air friction _______ weight of skydiver, F net = _______. Therefore, according to F net = ma, acceleration (a) = ______. Skydiver has reached _____________.

Velocity vs Acceleration BEFORE reaching terminal speed, the speed of skydiver _____ as he falls. BEFORE reaching terminal speed, the acceleration of skydiver ____ as he falls.

Pulling Parachute? After pulling parachute, what happens to force of air friction on skydiver? What does parachute change about skydiver? What happens to speed of skydiver after pulling chute? What is direction of acceleration after pulling chute? Which way does skydiver move after pulling chute relative to ground?

Who will hit ground first?

Friction

2 Types of Friction Static (F fs ) Kinetic (F fk ) or sliding

Static F f

Example 1 A 10kg crate is pushed along floor with a force of 60N. If coefficient of kinetic friction is 0.35, find acceleration of crate.

It requires a force of 175N to push a 50kg box across the floor at constant speed. Determine the coefficient of kinetic friction. Example 2

b) What if it is pushed with 700N to the right? Describe the motion. Example 3 The coefficient of static friction is A refrigerator weighs 1000N. a) What minimum force is needed to move the refrigerator?