Motion: Distance and Displacement Chapter 11 Section 1

What is motion? Can you see motion? Do you have to be able to see it for it to be happening? Are you moving now? Am I? Close your eyes.

Motion occurs when: An object changes its position.

Motion is relative. You are moving relative to the Sun and other planets even though maybe you aren’t moving in relation to your desk.

Frame of Reference Necessary to describe an object’s position Movement in relation to a frame of reference is relative motion

Distance How far an object has moved. Length of a path between two points.

Distance Measured in meter, kilometer, centimeter, millimeter

Scalar Quantities A scalar quantity can be described by magnitude (amount) only and has no direction. Time, distance, and volume are scalar quantities.

Displacement Distance and direction of an object’s change in position from the starting point. If distance is 20 meters, displacement might be 20 meters south (distance and direction).

Vector Quantity Displacement is a vector quantity. It has both magnitude and direction

The bell rings. Jenny gets up from her desk and walks 10 meters down the hall to her next class. She then realizes that her next class is in the same classroom she just left. So she turns around and walks 10 meters back to the same desk.

Jenny’s trip: Distance she traveled is? 20 meters Her displacement is? ZERO! She’s right back where she started from!

Practice on paper! Draw this: Exercise 1: John walks east 5 meters, then turns north and walks 2 meters, then turns west and walks 5 meters, and finally turns south and walks 2 meters. What is John’s distance traveled and displacement?

Remember: Distance is how far something has moved. Displacement is how far and what direction something is from its starting point!

Motion: Speed and Velocity Chapter 11 Section 2

Then what is Speed? Speed is the distance an object travels per unit of time. (per min. or per hour) Speed is the rate at which distance is traveled or the rate of change in position.

Think about your parents’ car: What is a standard speed on a city street? What about on I-40? You give speed as miles per hour, don’t you? Distance/time

The formula for speed is: speed = distance time or s = d t

When you set your car on cruise control, It can move at a constant rate of speed.

But think about riding your bike: What is about to happen to this girl’s speed on her bike?

What about NOW? Speed is not always constant! One of these guys is now WALKING his bike!

How do you talk about the speed of that bicycle? Two ways: Average speed Instantaneous speed

Average Speed Total distance traveled divided by the total time of travel S = d = 2 km = 4 km/h t .5 h

Instantaneous speed Speed at any given point in time If you look at the speedometer in your car and it say 55 m/h, that is your instantaneous speed at that exact moment.

We can GRAPH changing speed: What kind of graph would you use? Bar graph, Line graph, or Pie (circle) graph?

You can graph a change in distance: time (s) 0 1 2 3 4 5 distance (m) 0 20 50 130 150 200

So, now you know what speed is S = d t And how to graph it. (with a line graph)

But what about “velocity”? The best example of velocity is learning how to track a hurricane.

Velocity Is given in meters/second or m/s Velocity must include both speed and direction of motion. Ex: 20 mph east Is given in meters/second or m/s

Motion: Acceleration Chapter 11 Section 3

Section 3: Acceleration Acceleration is the rate of change of velocity. Can be a change in how fast something is going OR a change in direction.

Acceleration has one twist! Getting fast = positive acceleration Slowing down = negative acceleration!

Calculating Acceleration Acceleration =change in velocity time Change in velocity = final velocity minus initial velocity

a = (vf - vi) Acceleration t Acceleration is given in m/s/s or m/s2 _________________________________________________________ t Acceleration is given in m/s/s or m/s2

Forces and Motion Chapter 12 Section 1

Sect. 3—Motion and Forces Force—a push or pull that one body exerts on another What are some examples? Force can cause change in motion

A force is a push or a pull. Net Force A force is a push or a pull. A force of some kind is always required to change the state of motion of an object.

Measuring Force The scientific unit of force is the newton, abbreviated N. Force is measured most often using spring scale.

Net Force The combination of all forces acting on an object is called the net force.

Balanced and Unbalanced Force When two or more forces are acting on an object, we look at the NET FORCE Balanced forces cancel each other out-- Sum F = 0 Balanced forces = NO change in movement

Net Force The net force depends on the magnitudes and directions of the applied forces.

Net Force The net force depends on the magnitudes and directions of the applied forces.

Net Force The net force depends on the magnitudes and directions of the applied forces.

Net Force The net force depends on the magnitudes and directions of the applied forces.

Net Force The net force depends on the magnitudes and directions of the applied forces.

Net Force The net force depends on the magnitudes and directions of the applied forces.

If forces are balanced… Net force is zero. Forces are equal and opposite in direction. No change in motion.

Net Force When the girl holds the rock with as much force upward as gravity pulls downward, what is the net force on the rock?

Unbalanced forces If one force is larger than the other Movement occurs in the direction of the larger force

Force is an example of a vector quantity. Force Vectors A vector can be represented by an arrow that shows the magnitude and direction of a quantity. Force is an example of a vector quantity.

This vector represents a force of 60 N to the right. Force Vectors This vector represents a force of 60 N to the right. N

Force Vectors This vector shows two forces at work: NET FORCE

Newton’s First Law of Motion Inertia—the tendency of an object that is at rest to stay at rest, or if in motion to stay in motion UNLESS some force acts on it

Inertia—Newton’s 1st The object will keep moving in the same direction and at the same speed unless something makes it change The velocity won’t change

Have you ever felt inertia??? In a car? During a quick turn? During a fast stop?