Year 9 Revision Forces (1)

Year 9 Revision: Forces

1. Calculating Average Speed

  • Formula: Average Speed (m/s) = Distance travelled (m) / Time (seconds)

  • Example: A greyhound runs 400m in 25 seconds.

    • Calculation: Speed = 400m / 25s = 16 m/s

  • Rearranging the Equation:

    • To find Distance: Distance (m) = Speed (m/s) × Time (seconds)

    • To find Time: Time (seconds) = Distance (m) / Speed (m/s)

2. Calculating Acceleration

  • Definition: Acceleration occurs when an object's speed changes.

  • Formula: Acceleration (m/s²) = (Final speed (m/s) - Starting speed (m/s)) / Time taken (seconds)

  • Notes:

    • A negative answer indicates deceleration.

    • m/s² represents the rate of increase in speed per second.

  • Example: An arrow reaches a speed of 50m/s from rest in 0.1 seconds.

    • Calculation: Acceleration = (50m/s - 0m/s) / 0.1s = 500 m/s²

3. Tasks on Speed

  1. Racehorse: Travels 440m in 20 seconds. Find speed.

  2. Swift: Travels 120m in 3 seconds. Find speed.

  3. Racing Pigeon: 4800m in 2 minutes. Find speed (convert time to seconds).

  4. Tuna: Speed 20m/s; distance over 200 seconds?

  5. Tiger Beetle: Speed 12m/s; distance over 5 minutes?

  6. Quarter Horse: Speed 24m/s; time to run 400m?

  7. Car: Speed 30m/s; time to travel 100km?

4. Tasks on Acceleration

  1. Hammer: Dropped from rest, reaches 0.8 m/s in 0.5 seconds. Find acceleration.

  2. Motorcycle: Starts from rest, reaches 27m/s in 3.5 seconds. Find acceleration.

  3. Car: Travelling at 25m/s, comes to rest in 5 seconds. Find acceleration.

  4. Cat (Poppy): Running at 5m/s, accelerates to 10m/s in 2 seconds. Find her acceleration.

5. Distance-Time Graphs

  • Characteristics:

    • Horizontal Line = Object at rest.

    • Diagonal Line = Object moving at constant speed (steeper = greater velocity).

  • Acceleration: Change in gradient illustrates acceleration.

  • Average Speed Calculation: Total distance / Total time.

6. Speed-Time Graphs

  • Characteristics:

    • Constant Speed = Horizontal Line.

    • Accelerating Movement = Upward Line with Increasing Gradient.

    • Deceleration = Downward Line.

  • Gradient: Represents acceleration.

7. Tasks on Distance-Time Graphs and Speed

  • Example from Data:

    • Distance results from a student walking: Create a graph; calculate speeds.

  • Car Speed Data: Show graph; calculate acceleration; analyze area under graph for distance traveled.

8. Resultant Forces

  • Balanced Forces: Object at rest or moving at constant speed (no resultant force).

  • Unbalanced Forces: Resultant force present leads to acceleration.

  • Newton’s First Law: An object remains at rest or in constant motion unless acted on by a resultant force.

9. Tasks on Resultant Forces

  1. Analyze car speed graph; identify when forces are balanced or unbalanced.

  2. Anchor: Moving at constant speed - what does that mean for forces?

  3. Rocket: Accelerating upwards - implications for forces?

  4. Aircraft: Landing and decelerating - assess forces.

10. The Cantilever Experiment

  • Objective: Investigate how weight affects sag and the position of force.

  • Variables:

    • Independent: Pulling force.

    • Dependent: Sag.

    • Control: Position of the force.

  • Data Representation: Line graph; calculate mean.

  • Direct Proportionality: Straight line through the origin indicates a direct relationship.

11. Tasks on the Cantilever

  • Identify variables in the sag experiment; calculate mean sag.

  • Assess if results are directly proportional and determine gradient for predictions.