Describing Motion Ch. 3 & 4 Motion & Forces Motion & Speed (3.1) Velocity (3.2) Acceleration (3.2)

Newton’s First Law Newton’s First Law of Motion An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force. motion constant velocity net force

Motion 3.1 Problem: Is your desk moving? We need a reference point... nonmoving point from which motion is measured

Motion Motion Change in position in relation to a reference point.

Motion Problem: You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward. You have mistakenly set yourself as the reference point.

Speed Speed rate of motion distance traveled per unit time

Speed Instantaneous Speed speed at a given instant Average Speed

Calculations d = 100 m v = d ÷ t t = 20 s v = (100 m) ÷ (20 s) v = ? Your neighbor skates at a speed of 4 m/s. You can skate 100 m in 20 s. Who skates faster? GIVEN: d = 100 m t = 20 s v = ? WORK: v = d ÷ t v = (100 m) ÷ (20 s) v = 5 m/s You skate faster!

Calculations Florence Griffith Joyner set a world record by running 200 m in 21.34s. What was her average speed? Answer: 9.37 m/s

Calculations v = 330 m/s t = d ÷ v d = 1km = 1000m Sound travels 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for you to hear it? GIVEN: v = 330 m/s d = 1km = 1000m t = ? WORK: t = d ÷ v t = (1000 m) ÷ (330 m/s) t = 3.03 s

Work the practice problem p. 67 Answer: 21.9s

Graphing Motion slope = speed steeper slope = straight line = * 07/16/96 Graphing Motion Distance-Time Graph A B slope = steeper slope = straight line = flat line = speed faster speed constant speed no motion *

Graphing Motion Who started out faster? A (steeper slope) Distance-Time Graph A B Who started out faster? A (steeper slope) Who had a constant speed? A Describe B from 10-20 min. B stopped moving Find their average speeds. A = (2400m) ÷ (30min) A = 80 m/min B = (1200m) ÷ (30min) B = 40 m/min

Design a Slow Flyer p. 70 You will be designing a paper air plane to fly as slow as possible Form a hypothesis What factors might contribute to a slow flying plane? How will we calculate the speed? Design a set of rules Flight location, distance, launching method…

Velocity and Acceleration p. 72

3.2 Speed & Velocity Problem: A storm is 10 km away and is moving at a speed of 60 km/h. Should you be worried? It depends on the storm’s direction!

Speed & Velocity Velocity speed in a given direction can change even when the speed is constant!

Acceleration Acceleration the rate of change of velocity change in speed or direction a: acceleration vf: final velocity vi: initial velocity t: time

Acceleration Positive acceleration “speeding up” Negative acceleration “slowing down”

Calculation s a = (vf - vi) ÷ t t = 3 s a = (32m/s - 10m/s) ÷ (3s) A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration? GIVEN: vi = 10 m/s t = 3 s vf = 32 m/s a = ? WORK: a = (vf - vi) ÷ t a = (32m/s - 10m/s) ÷ (3s) a = 22 m/s ÷ 3 s a = 7.3 m/s2

Calculations t = ? t = (vf - vi) ÷ a t = (0m/s-30m/s)÷(-3m/s2) How long will it take a car traveling 30 m/s to come to a stop if its acceleration is -3 m/s2? GIVEN: t = ? vi = 30 m/s vf = 0 m/s a = -3 m/s2 WORK: t = (vf - vi) ÷ a t = (0m/s-30m/s)÷(-3m/s2) t = -30 m/s ÷ -3m/s2 t = 10 s

Graphing Motion Distance-Time Graph Acceleration is indicated by a curve on a Distance-Time graph. Changing slope = changing velocity

Graphing Motion acceleration slope = + = speeds up - = slows down Speed-Time Graph acceleration + = speeds up - = slows down slope = straight line = flat line = constant accel. no accel. (constant velocity)

Graphing Motion Specify the time period when the object was... Speed-Time Graph Specify the time period when the object was... slowing down 5 to 10 seconds speeding up 0 to 3 seconds moving at a constant speed 3 to 5 seconds not moving 0 & 10 seconds

Defining Force (3.4) Forces Friction Ch. 3.4 Motion & Forces Defining Force (3.4) Forces Friction

Force Video Before the video: Complete the pretest During the video: * 07/16/96 Force Video Before the video: Complete the pretest During the video: Complete the video review After the video: Complete the post test VL Force newton.pdf and video *

Force Video

Force Fkick Fgrav Force a push or pull that one body exerts on another What forces are being exerted on the football? Fkick Fgrav

Force Balanced Forces forces acting on an object that are opposite in direction and equal in size no change in velocity

Balanced Forces

Force Net Force unbalanced forces that are not opposite and equal velocity changes (object accelerates) Fnet Ffriction Fpull N W

10N-7N = 3N causes change in velocity. Net Force - Unbalanced 10 N 7 N Net Force 10N-7N = 3N causes change in velocity.

Newton’s First Law Newton’s First Law of Motion An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force.

Newton’s First Law Newton’s First Law of Motion “Law of Inertia” tendency of an object to resist any change in its motion increases as mass increases

Which has more inertia?

Friction Friction force that opposes motion between 2 surfaces depends on the: types of surfaces force between the surfaces

Friction Friction is greater... between rough surfaces when there’s a greater force between the surfaces (e.g. more weight) Pros and Cons?

Gravity/Weight 3.5

Gravity Gravity force of attraction between any two objects in the universe increases as... mass increases distance decreases

Gravity Who experiences more gravity - the astronaut or the politician? Which exerts more gravity - the Earth or the moon? more mass less distance

Weight The measure of the force of gravity on an object Not the same as mass Your mass would be the same on the moon but your weight would be less!

Weight Mass- the amount of matter in an object Measured in kg Weight is a force Measured in newtons (N) 1 kg of mass on earth’s surface weighs 9.8N

Gravity Would you weigh more on Earth or Jupiter? Jupiter because... greater mass greater gravity greater weight