Grade 8 -Lesson 3 — Acceleration Page 312
- What are the three ways an object can accelerate?
- What does a speed-time graph indicate about an object’s Motion?
Acceleration is the measure of the change in velocity during a period of time.
- When does an object accelerates?
- Object accelerates when its velocity changes due to:
- Increasing speed
- Decreasing speed
- Changing direction
- Example: Roller Coaster
- Drop down— reach a faster speed quickly — it is accelerating because its speed
- Changes direction — it is accelerating because it changes direction.
- Time the velocity changes it accelerating page 313.
How do we represent Acceleration?
- Can be represented by an arrow.
- The length of the arrow indicates amount of acceleration
- Can also show direction
- When speeding up
- The initial velocity is represented by the slower arrow.
- The final velocity is represented by the longer arrow.
- The acceleration arrow is facing or pointing towards the final velocity.
- When slowing down
- The initial velocity is represented by a longer arrow.
- The final velocity is represented by a shorter arrow.
- The acceleration arrow is facing or pointing toward the initial velocity.
- Constant Speed — velocity arrow will be the same length during the entire change of direction.
- The car’s velocity changes because it's direction changes.
- Notice that the car is accelerating toward the inside of the curve.
- Look at the length of the velocity arrows.
How do we calculate acceleration?
- Acceleration is a change in velocity divided by the time interval during which the velocity changes.
- Velocity is the speed of an object in a given direction.
- Positive acceleration is the speeding up in the forward direction.
- Negative acceleration is slowing down in the forward direction as well as speeding up in the reverse direction.
- Speed Time graph has time on the horizontal axis or X-axis.
- Speed is located on the Vertical Axis or Y-axis.
Objects at rest
- Is not moving.
- In speed time graph - an object at rest is a horizontal line at y=0.
- For constant speed the plotted line is horizontal.
- If the line is farther from the x axis, the object is moving at a faster speed.
Homework: Page 317 — Speeding up
Page 318 - entire page
Speeding Up p. 317
- If a object increases its speed at a steady rate — How would it look on a speed time graph?
- Draw the speed time graph (pictured on bottom of page 317)
Slowing Down page 318
- If an object decreases its speed at a steady rate — How would it look on a speed time graph?
- Draw the speed time graph (pictured at the top of page 318).
- When the line touches the x-axis, the speed is zero.
Limits of Speed Time Graphs
- Speed Time Graphs show the speed of an object.
- Speed Time Graphs do NOT show the direction that the object is moving.
- Speed Time Graphs show only the relationship speed and time.
- Speed Time Graphs do not show a change in velocity. (The velocity will change as a result of direction).
- Walk down the hallway.
- Position — noted by direction and distance from a reference point
- Average speed is calculated by distance and displacement.
- Velocity is calculated by the speed and direction.