1. UNIT 2
FORCE & MOTION

2. Motion Objects move in a variety of ways!
How do we know when an object is moving?
Constant motion - an object covering equal distances in equal amounts of time: constant speed
Non-constant motion - an object doesn’t cover equal distances in equal intervals of time
An object is moving if its position changes; does the background change?
Speed describes how fast an object moves.
FORCE & MOTION

3. What is Speed? Speed measures motion. To determine speed you must
Measure the distance traveled by an object
Measure the time it takes to travel that distance
FORCE & MOTION

4. Determining Speed?
Don’t forget to use International Scientific Units or SI units!
How fast an object moves in meters per second (m/s) “rate of motion.”
A change in position from one place to another in any direction is described as motion. (meters or kilometers)
The length of time that it takes for that change to occur, or the rate of change in position is described as speed. (seconds or hours)
FORCE & MOTION

5. Types of Speed
Average speed – distance covered by an object divided by the time it takes to travel that distance
Instantaneous speed – speed measured at any given instant
Constant speed – when speed doesn’t vary over a long period of time
Negative acceleration – slowing down
Positive acceleration – speeding up
Resting objects - speed of 0 m/s
FORCE & MOTION

6. Speed & Velocity SPEED – how fast an object moves
VELOCITY – describes both speed and direction d
s t
Speed =d/t
Define and practice and more Velocity practice
Define and practice -
Velocity practice is
FORCE & MOTION

7. Velocity example
FORCE & MOTION

8. Velocity example
FORCE & MOTION

9. Momentum Moving objects have momentum
Momentum depends on both its velocity and its mass
Momentum has direction; an objects momentum is in the same direction as its velocity
If a train and a car are moving at the same velocity, which one has the greater momentum?
FORCE & MOTION

10. Measuring Momentum
The more mass an object has, the greater its momentum (for a given velocity)
The faster an object is moving, the greater its momentum
Momentum is zero if an object isn’t moving
SI unit is kilograms times meters per second (kg*m/s)
FORCE & MOTION

11. Momentum Equation For momentum momentum = mass x velocity p = m*v p
Definition
Youtube spaceship battle
(Can’t see at school)
Definition - ntumDefinition1.html
Youtube spaceship battle -
FORCE & MOTION

12. Momentum example
FORCE & MOTION

13. Momentum example
FORCE & MOTION

14. Momentum example
FORCE & MOTION

15. Acceleration The rate at which velocity changes –not speed!
When an object speeds up then acceleration is in the same direction as velocity. When an object slows then acceleration is in the opposite direction as that of velocity.
FORCE & MOTION

16. Car acceleration
Press on the gas – car speeds up – acceleration is in the direction of the car’s motion
Press on the brake – car slows down – acceleration is opposite to the car’s direction
Turn the steering wheel – changes velocity even if speed doesn’t change – acceleration changes
FORCE & MOTION

17. Acceleration formula Acceleration = change in velocity/time v a t
Change in velocity = final velocity – initial velocity
v = vF - vI
a = v/t
FORCE & MOTION

18. Acceleration example
FORCE & MOTION

19. Practice Acceleration definition and practice Line Rider 2
Definition from Physics Textbook
Notes and practice
Acceleration def and practice-
Line Rider 2 -
Def from Physics text -
Notes and practice - ation.html
FORCE & MOTION

20. Force
A force can most easily be described as a push or a pull. When a force is applied to an object, the velocity of that object changes. This change in velocity constitutes an acceleration. So, forces are tied to accelerations.
FORCE & MOTION

21. Force
Net force – combination of all of the forces acting on an object, determines whether the velocity of the object will change
An object accelerates in the direction of the net force; kicking a ball
Balanced forces completely cancel each other and the combined force equals zero; tug-of-war where rope doesn’t move
Force and Motion Experiments
Force = f
mass * acceleration m a
Force and Motion Experiments -
FORCE & MOTION

22. Force - Balanced
Forces on an object that are equal in size and opposite in direction are balanced forces and will not change the velocity of an object
FORCE & MOTION

23. Force - Unbalanced
When the forces become unbalanced the NET FORCE applied to the object will always change the velocity of the object by changing its speed or direction.
FORCE & MOTION

24. Friction
Friction is a force that opposes motion between two surfaces that touch.
The amount of friction depends on the kinds of surfaces and the forces pressing the surfaces together.
FORCE & MOTION

25. Friction
If a ball is rolling across the floor, it will slow and stop. Force keeps the ball rolling and FRICTION is the unbalanced force acting against the ball’s direction of motion.
Friction affects non-moving objects. Friction of brakes balances the force of gravity and stops a parked truck from rolling down a hill.
Try walking on ice and on grass. You slip on ice because there is less friction between your shoes and the ground.
FORCE & MOTION

26. Friction (rolling, sliding,fluid)
Sliding friction is the strongest motion friction. Ex: push a box across the floor.
Rolling is used to reduce sliding friction. Ex: wheels
Fluid friction is from fluid or gas. It reduces air resistance. Oil reduces sliding friction. Ex: WD40 on a door hinge
FORCE & MOTION

27. Air resistance Another type of friction
The amount of air resistance on an object depends on its size and shape as well as on the speed with which it moves.
Objects with larger surfaces have greater air resistance. Air resistance also increases as the objects speed increases.
FORCE & MOTION

28. Gravity
Gravity is a force. Every object in the Universe exerts a force of gravity on every other object.
The amount of gravity depends on mass and distance. The more mass an object has and the closer the distance to another object the more gravitational force.
Gravity website and games
Gravity website and games -
FORCE & MOTION

29. Gravity Example
FORCE & MOTION

30. Weight
The measure of the force of gravity on an object is the object’s weight. Weight refers to gravitational force between earth and a body at Earth’s surface. If a person weighs 100 pounds the Earth’s gravity is exerting 100 pounds of force on that person. The moon has a weaker gravitational force than the Earth because it doesn’t have the mass of the Earth.
FORCE & MOTION

31. Weight formula Weight = mass * gravity w m g Gravity = 9.8 m/s2
Weight is measured in Newtons w
m g
FORCE & MOTION

32. Free fall Caused by gravity
Objects experience air resistance which is fluid friction
Acceleration due to gravity is 9.8 m/s2
FORCE & MOTION

33. Newton’s Three Laws
Cool website
1st Law -An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called "the law of inertia".
2nd Law -Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
3rd Law -For every action there is an equal and opposite re-action.
Cool website -
FORCE & MOTION

34. Remember the Laws? 1st Law 2nd Law 3rd Law FORCE & MOTION
Demonstration
FORCE & MOTION

35. Newton’s Laws of Motion
Definition
Simplified
NASA site to visit
Explanation
Demonstrations
Detailed information
Definition -
Simplified -
NASA site to visit -
Explanation -
Demonstrations -
Detailed information -
Brainpop - subscription site
FORCE & MOTION