USV: Physical Science: Forces Forces & motion USV movie: Physical Science: Forces Begin with pg 420 – spring activity & do how to read science….WKST USV: Physical Science: Forces

FORCE A push or a pull How can you tell those objects are exerting a force on each other? What are other examples of forces? How do you know a force exists if you can’t see it? Feel effects , see movement Tennis racket and ball picture Magnets – feel the force Baseball and bat Wind on sailboat Cant see but can see effects of it if static charges

FORCE Forces are measured in NEWTONS (N) 1N is the force needed to change the speed of a 1-kg object by 1m/s Measure with a spring scale How do you know a force exists if you can’t see it? Feel effects , see movement Tennis racket and ball picture Magnets – feel the force Baseball and bat Wind on sailboat Cant see but can see effects of it if static charges

Think-Pair-Share Discuss with your table partner situations you encountered today where you saw evidence of a forces being exerted. Be sure to describe the source of the force. Give at least two examples.

Forces on Objects UNBALANCED FORCE = movement of an object An object at rest will move A moving object will change or stop BALANCED FORCE = equal forces acting in opposite directions that causes no change in motion Net for 0 if balanced Worksheet

Forces on Objects Combinations of forces will determine the effect of forces NET FORCE = combination of all forces acting on the object Net for 0 if balanced Worksheet

60 N 100 N up 100 N down 20 N up 20 N down 40 N

60 N 150 N up 150 N down 90 N up 90 N down 30 N up 30 N down 50 N 40 N

Friction Force between surfaces that resists the movement of one surface past the other surface Ice skates on ice Tires and the road Rougher surface = more friction Do marbles thing with book first Stops objects from being in motion Bumpy roads

3 types of friction Rolling – resists the motion of a rolling object Sliding – resists the motion of a sliding object Static – resists the motion of an object Rolling – skateboard’s wheels Sliding – pushing a box across the floor Static –initial movement

Friction Good: Bad: Feet & ground Wheels & ground Keeps you on the scooter Bad: Wind and soil = erosion Causes heat that can make engines run less efficiently Can wear things down Do marbles thing with book first Stops objects from being in motion Bumpy roads

GRAVITY Force of attraction that exists between any two objects Pull of gravity depends on 1. MASS of object greater mass = greater gravitation force MASS = amount of matter in an object 2. The closer the centers of the two objects are, the greater the force

GRAVITY A. B. Which of the following has more pull of gravity? 15 m 5 kg 5 kg 15 m 10 kg 10 kg 2nd has greater gravity because of bigger mass

GRAVITY A. B. Which of the following has more pull of gravity? 15 m 5 kg 5 kg 20 m 5 kg 5 kg 1st has greater gravity because they are closer

GRAVITY & the Universe Pages 430-431 Gravity determines the motion of the planets and stars The moon’s gravity causes the tides in Earth’s oceans Moon pulls the water away from the Earth on one side & pulls Earth away from water on the other side

Think about this… The moon affects the tides more than the sun does because… The sun is closer to the Earth than the moon The sun is more massive than the moon The moon is closer to the Earth than the sun The moon is more massive than the sun C

WRITING FOR SCIENCE Imagine that you live on Mars. The gravity is about ½ of our gravity here on Earth. Write a description of how the reduced gravitational force would affect your everyday activities. This should be interesting!

What are the different frames of reference in this picture? DESCRIBING MOTION FRAME OF REFERENCE = the object an observer uses to detect motion Seat on a roller coaster The sun Your mailbox Ask questions from book What are the different frames of reference in this picture?

DESCRIBING MOTION RELATIVE MOTION = the change in position of one object compared to the position of another object So, we can’t feel that we are moving 1600 km/hour due to the Earth’s rotation because the Earth is moving too! What does looking at the sun tell us? If we look at the sun’s position we see us moving

DESCRIBING MOTION 3 TYPES OF MOTION Vibrational = rapid back and forth movement – drum cymbals Circular = motion around a central point – yo-yo Straight line = motion in a line Vibrational – eardrum, speakers, instrument strings Circular – planets around the sun, bike wheel, amusement ride Straight – jet plane walking cars driving

To Review Circular Straight line Vibrational Eardrum gathering sound Bike wheel Speakers Walking Movement of a planet Cars driving Violin strings Circular Straight line Vibrational

DESCRIBING MOTION SPEED = the distance an object moves in a certain period of time Speed = distance/time INSTANTANEOUS SPEED = speed at any given point Checked with a SPEEDOMETER VELOCITY = a measure of both the speed and direction of a moving object 10 meters per seconds north Use example from book Problem on 434

DESCRIBING MOTION ACCELERATION = the change in velocity during a particular time period Speeding up Slowing down Changing direction Results from unbalanced forces acting on the object When is an airplane accelerating – Takeoff, turning, landing Worksheets

DESCRIBING MOTION Speed= distance ÷ time Distance = speed x time Time = distance ÷ speed How long would it take me to travel 20m on my bike if I my speed was 5 m/hr? 25 hr 100 hr 4 hr Worksheet C

NEWTON’S LAWS

Sir Isaac Newton 1660’s English scientist LAW = statement that describes events or relationships that exist in nature Newton formed laws based on experiments & observations about how things move in ideal conditions Many experiments that were first theories

NEWTON’S 1st LAW Objects resist changes in motion Object at rest stays at rest unless acted on by an unbalanced force Object in motion continues in motion unless acted on by an unbalanced force Book on table In ideal conditions

NEWTON’S 1st LAW INERTIA = the tendency of an object to resist any change in its state of motion More mass = more inertia Heavier things are harder to stop Jar of pennies verses jar of feathers

NEWTON’S 1st LAW What is it like in outer space? Why do we wear seat belts? Space is closer to ideal conditions, less gravity Because you are an object in motion

NEWTON’S 2nd LAW An object’s acceleration depends on the mass of the object and the size and direction of the force acting on it. Force = mass x acceleration Read B99

NEWTON’S 2nd LAW I would need to exert a large force to move a large mass I would need to exert a small force to move a small mass Read B99

NEWTON’S 2nd LAW Objects accelerate in the direction of the force that acts on them As acceleration is changing, force must also be changing Read para 1 on B103

NEWTON’S 2nd LAW You are riding on a bicycle. You stop to place a heavy object on the back of the bike. How will the increased mass affect the bike’s acceleration if you pedal with the same force? It will decrease It will stay the same It will increase a

NEWTON’S 3rd LAW When a force is applied to an object, the object exerts an equal force in the opposite direction Law of action and reaction 440 When 1 object exerts a force on 2nd object, 2nd object exerts and = and opp. Force on first object When you walk – foot pushes on ground, ground pushes back or it would push away and we would fall

Momentum Depends on its mass and velocity             Depends on its mass and velocity The more momentum an object has, the harder it is to stop Momentum is transferred when objects collide

Momentum             Law of Conservation of Momentum says that momentum before the collision is equal to momentum after the collision Newton’s cradle

To Review Which has greater momentum, a car sitting still or a pebble rolling down a hill? Car Pebble

To Review An adult and a child are ice skating. The child pushes away from the adult. The child moves backward. What will happen to the adult? Nothing The adult will move in the same direction as the child The adult will move in the opposite direction from the child

To Review You apply a force to a soccer ball when you kick it. Compare this force to the force that the soccer ball exerts on your foot. The soccer ball exerts a weaker force on your foot in the opposite direction The soccer ball exerts the same force on your foot in the opposite direction The soccer ball exerts a weaker force on your foot in the same direction