1. 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

2. 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

3. 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

4. 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.

5. 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

6. 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

7. 60 N
100 N up
100 N down
20 N up
20 N down
40 N

8. 60 N
150 N up
150 N down
90 N up
90 N down
30 N up
30 N down
50 N
40 N

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. GRAVITY & the Universe
Pages
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

16. 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

17. 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!

18. 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?

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. NEWTON’S LAWS

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

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

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

38. 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

39. 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