Day 4 At A Glance We have one goal for today: 1) Start Graph Boot Camp This will be a BIG learning session about graphs, how to use them, and their relationship to physics. You will also be better prepared to deal with math class and the SAT’s

TRUE OR FALSE, AND WHY? 1) A car that is slowing down has a negative acceleration A ball thrown down from the top of THS will gain more speed per second than a ball dropped from the top of THS.

TRUE OR FALSE, AND WHY? 1) If an object is accelerating, then the velocity of the object can never be zero at any time. If an object has a velocity of zero for a moment, its acceleration at that moment is zero.

TRUE OR FALSE, AND WHY? 1) If an object keeps the same ‘speed’ or magnitude but changes direction, there is an acceleration. If an objects acceleration is constant, then it must stay in the same direction.

TRUE OR FALSE, AND WHY? 1) If an object is thrown up hard enough, it will no longer come back down. If you throw an object hard enough, gravity will not slow it down at all.

Try The Math A car accelerates from rest at +4 m/s2 for 2 seconds. How fast will it be going at that time? Key idea: REST means V is 0. Not overall, just Vi or Vf depending on the words. Look at m/s, s, m/s2 or m to figure out what is given!

The Key Ideas 1) 3 things you can do with graphs 2) What are the 3 types of graphs, and how do you tell? 3) The relationship between d, v and a

GRAPH BOOT CAMP Basic Training: The facts Position-Time Graph Position Velocity Read the Y axis Take the slope for the time period needed Velocity-Time Graph Velocity Acceleration Displacement Read the Y axis (above x axis is +) Take the slope for the time period needed Find the area between the line and the x axis (you cannot find the actual position, just the amount changed)

2nd Scenario For Review - VOTE A person is on a track starting at rest and accelerates to a fast + velocity. Which is the correct position vs. time graph?

LETS SEE Summary of graph: Displacement is + but is decreasing , so object starts far from the reference point and is approaching it.

LETS SEE…VOTE A) The object starts off very fast in the + direction, slows and comes to a stop B) The object starts off very fast in the – direction, slows and comes to a stop C) The object starts off at rest and speeds up to a fast + velocity D)The object starts off at rest and speeds up to a fast – velocity

LETS SEE What does the velocity graph look like? v

You should be drawing all kinds of lines on graphs, either to find slopes or make geometric shapes for areas. If values are not provided (happens a bunch), its about trends than actual values. Draw LOTS of short slope lines to see trends

ANSWER…BUT WRITE DOWN WHY! 1) You start off walking away from your front door. You start off slow and eventually end going very fast. 2) You start off running away from your front door. You start off fast and eventually end up walking slow.

To The Board! You will draw three graphs with me to show you are understanding this. Scenario: Toss pen up in air, it comes back down to your hand. Draw the position-time graph. Circle where the max height occurs Next to it write an explanation on why it is shaped the way you drew it.

MY GRAPH

WHY? Went back into your hand….Overall displacement is ZERO. So the graph starts and ends at the same place. End up HIGH at the max height. That’s the tallest part of the graph. Never NEGATIVE because it does not go below your starting point (hand). Its CURVED because of acceleration.

To The Board! Scenario: Toss pen up in air, it comes back down to your hand. Draw the velocity-graph. Circle where the max height occurs Next to it write an explanation on why it is shaped the way you drew it.

MY GRAPH

WHY? Starts off + because going up. Taking the slopes of parts of the graph told us that. / Gets less + because the slopes become flatter At the top its 0 because the slope at that point is FLAT. Becomes more and more – because the slopes are more \ .

To The Board! Scenario: Toss pen up in air, it comes back down to your hand. Draw the acceleration-time graph. Next to it write an explanation on why it is shaped the way you drew it.

MY GRAPH

WHY? Because the slope of velocity is a straight line. So it’s a non-changing value. And its – because its sloped like \ Its gravity!

MAJOR CONCLUSIONS! Because the slope of velocity is a straight line. So it’s a non-changing value. And its – because its sloped like \ Its gravity!....Back to your seats

My Turn At 4 seconds how far are you from the start? What is your average velocity during that time? How far did you go from 4 to 8 seconds? What would your average velocity be during that time?

Notice its curved…what does that tell us? 1) There is an acceleration. 2) Since the curve is upwards, it’s a + acceleration. 3) The velocity graph starts at low + and increases

Lets Do Some HW… 1st try it at your tables. If having issues, take it to the boards. Goal: To not only do it, but understand WHY!