1. Motion and Forces

2. Motion Motion- A change in position in a certain amount of time
In order to describe motion, you need a frame of reference to compare it with
Motion

3. Speed Speed = Distance Time Speed- The rate at which an object moves
Velocity- Speed in a given direction
Since distance is usually measured in meters and time in seconds, the unit for speed is given in meters per second (m/sec)
Speed = Distance
Time

4. Measuring Speed
If a car travels 500 meters in 20 seconds, what is its speed?
500 meters
20 seconds
Speed = distance = 500 meters = 25 m/sec
time seconds
What is the speed of a jet plane that travels 7200 km in 9 hours?
Speed = 7200km / 9 hr = 800 km/hr
The speed of a cruise ship is 50km/hr. How far will the ship travel in 14 hours?
Distance = Speed x time
= 50km/hr x 14 hrs
= 700 km

5. Acceleration Acceleration- The rate in change of velocity
If something is accelerating, it is speeding up, slowing down, or changing direction
The acceleration of an object is equal to its
change in velocity divided by the time in
which the change occurs
Acceleration = Final velocity – Original Velocity
Time

6. Determining Acceleration
A rollercoaster has a velocity of 10 m/sec at the top of a hill. Two seconds later it reaches the bottom of the hill with a velocity of 20 m/sec. What is the acceleration of the rollercoaster?
Acceleration = Final velocity – Original Velocity
Time
Acceleration = 20 m/ sec – 10 m/sec = 10 m/sec = 5 m/sec/sec
2 sec sec
A rollercoaster is moving at 25 m/sec at the bottom of a hill. Three seconds later it reaches the top of the next hill, moving at 10 m/sec. What is the deceleration of the rollercoaster?
Deceleration = Final velocity – Original Velocity
Deceleration = 10 m/ sec – 25 m/sec = -15 m/sec = -5 m/sec/sec
3 sec sec

7. The Nature of Force Net Force
The change in motion of an object is determined by the net force acting on the object. What is the net force for each situation?
0 N

8. The Nature of Force
Which of these three arrows represents the correct amount of net force of the above two arrows?

9. Friction and Gravity Types of Friction
Friction acts opposite the direction of motion. Determine the frictional force at work.

10. Friction and Gravity Frictions
Give five examples for sliding, static, fluid and rolling frictions.

11. Friction and Gravity Gravitational Attraction
Gravitational attraction depends on two factors: mass and distance. Compare the gravitational force between different planets and their sun.

12. Friction and Gravity Weight and Mass
The Mars Phoenix Lander weighs about 3,400 N on Earth. It weighs about 1,300 N on Mars. If the dog weighs
60 N on Earth, what would he weigh on Mars and the moon?

13. Laws of Motion Newton’s laws of motion describe three states of motion
Rest
Constant motion
Accelerated motion
The laws also explain how forces cause all of the states of motion

14. Newton’s first law of motion
The first law states that an object at rest will remain at rest and an object in motion will remain in motion at a constant velocity unless acted upon by an outside force
Since constant velocity means the same speed and direction, in order for an object to change velocity, or accelerate, a force must act on it
The concept of inertia forms the basis for this law
Inertia- the property of matter that tends to resist any change in motion
The inertia of an object is related to its mass
The more massive an object, the more inertia it has and the more difficult it will be to move
You feel the effects of inertia when you are riding in a car that stops suddenly while you keep moving forward

15. Newton’s second law of motion
The second law of motion show how force, mass, and acceleration are related
Force = Mass x Acceleration
When mass is measured in kilograms and acceleration in meters/sec/sec, force is measured in Newtons (N)
Tells us that a greater force is require to accelerate an object with a greater inertia (mass)
Explains one reason why smaller cars get better gas mileage than larger ones

16. Newton’s Laws of Motion
Newton’s Second Law
Suppose that four dogs pull a sled carrying two people. How can the picture-stories be completed to represent answers to the two different questions?

17. Newton’s third law of motion
States that for every action, there is an equal and opposite reaction
According to the third law:
Every force must have an equal and opposite force
All forces come in pairs
You demonstrate the third law when you walk
Your feet push against the floor
The floor pushes with an equal but opposite force against your feet
You move forward
The reaction engine utilizes the third law

18. Newton’s Laws of Motion
Action-Reaction Forces
How can the illustration of the dogs be completed to represent Newton's Third Law of Motion?

19. Newton’s Laws of Motion
What Makes a
Bug Go Splat?
Splat! A bug
has just flown into the windshield of
an oncoming
car. The car
must have hit
the bug much harder than
the bug hit
the car, right?

20. Free Fall and Circular Motion
Global Positioning Systems

21. Free Fall and Circular Motion
Complete the table below for an object that is dropped from rest.

22. Free Fall and Circular Motion
Satellite Motion
A satellite launched from Earth enters orbit because the curve of its path matches the curved surface of Earth. What is the gravitational force on the ball at each point?