1. Forces and Motion
Chapter 16

2. Motion Motion = a change in position
Motion is observed by comparing an objects position to a stationary object
Frame of reference = a stationary object used to determine a position change

3. Speed
Speed = the distance that something moves in a certain period of time
Example: Your family is taking a car ride for 80 miles and the trip takes 2 hours. What is the speed that your family was driving?

4. Velocity
Speed tells you how fast or slow an object is moving but it doesn’t tell you which direction the object moves in.
Velocity = the speed and direction of a moving object

5. Speed vs. Velocity Speed Velocity A truck is traveling at 31 mi/hr
A bird is flying at a rate of 2.3 km/min
A truck is traveling north at 31 mi/hr
A bird is flying east at a rate of 2.3 km/min

6. Speed Problems
What is the speed of a sailboat that is traveling 100 meters in 120 seconds?
2. Calculate the speed of a dog running through a field if he is covering 23.7 meters in 54 seconds.

7. Speed Problems
3. How long does it take a baseball traveling at a speed of 20.4 m/s to go 49 m?
4. A cross country runner runs at a speed of 2.6 m/s. How far will she run in 134 s?

8. Velocity Problems
5. Calculate the velocity of a car that travels 556 kilometers northeast in 3.4 hours.
6. If a projectile flies north 387 meters in 5.8 seconds, what is its velocity?

9. Force Force = a push or a pull
Forces cause a change in an object’s velocity
Examples:
Opening/closing a door
Gravity
magnetism

10. Acceleration
Acceleration = a change in velocity of an object divided by the time it takes for the change to occur

11. Force = mass x acceleration
The greater the force on an object, the greater its acceleration.
Example:
Lightly pushing a door to close it.
Slamming a door shut
Using the same amount of force, the greater the mass of an object the less it accelerates
Pushing an empty shopping cart
Pushing a filled shopping cart

12. Inertia
Inertia = the tendency of matter to resist a change in its state of motion
Law of Inertia = an object at rest stays at rest and in object in motion stays in motion unless acted on by an outside force.

13. Force problems
Your bicycle has a mass of 9.1 kilograms. You accelerate at a rate of 1.79 m/s2. Calculate the force that is accelerating the bicycle.

14. Force problems
2. The Space Shuttle has a liftoff mass of 2,041,000 kg and accelerates at a rate of 16 m/s2. Calculate the force that is accelerating the Space Shuttle.

15. Force problems
3. A runner has a mass of 89 kilograms. He produces a force of 84 Newtons between the ground and his running shoes. How fast does he accelerate?

16. HW
A man hits a golf ball (0.2 kg) which accelerates at a rate of 20 m/s2. Find the force on the ball.
2. You push a friend sitting on a swing who has a mass of 50 kg and accelerates at a rate of 4 m/s Find the force you exerted.
Calculate the acceleration of a car if the force is 450 Newtons and the mass is 1300 kilograms.

17. Balanced Forces
Balanced forces = equal forces that act in opposite directions
Cancel each other out
Object will not accelerate
Net force = total of all the forces acting on an object
Net force of balanced forces always = 0

18. Unbalanced Forces
Unbalanced force = forces that are acting on an object but do not cancel each other out.
Net force  0
Object will accelerate

21. Types of Forces Surface Tension Buoyant Force
Force that occurs at the surface of a liquid
Buoyant Force
Pushes upward on objects in a fluid

22. Types of Forces Nuclear Force Magnetic Force
Forces inside the nucleus that keep atoms together
Magnetic Force
Pulling or pushing force between 2 magnetic fields

23. Types of Forces Centripetal Force Electric Force
Force that acts between objects that have an electric charge
Opposite charges attract
Like charges repel
Centripetal Force
Force acting on an object that is following a curved path

24. Friction
Friction = a force that acts between any surfaces in contact with one another
Prevents motion or slows it down

25. Gravitational Force
Gravitation Force = a force that acts between any 2 masses in the universe and pulls them toward each other
No physical contact between the objects is required for gravity to exist

26. Gravity and Air Resistance
A force that works against gravity is air resistance.
As gravity pulls an object down, air resistance pushes an object up.
Air resistance depends on the size and shape of the object.

27. How Mass Affects Gravity
The more massive the objects, the stronger the gravitational force.
That’s why Earth pulls everything toward it, because it is so massive.

28. How Distance Affects Gravity
The closer 2 objects are to each other, the stronger the gravitational force between them.
That’s why Earth holds us down, but not things in outer space.

29. How Planets Move in Orbits
Why don’t planets just crash into the sun?
Two factors:
Sun’s gravity
Planet’s inertia

30. Gravity and Weight
Weight = a measure of the force of gravity on an object
Changes if gravity changes
Measured using a scale
Mass = the amount of matter in an object
Is not affected by gravity
Measured using a balance