Instructions: study the paragraphs and charts below and answer the questions.

Transcription

1 Speed, Velocity, and Acceleration Physical Science Name: Grade: Class Period: Date: Essential Question: What is the difference between speed, acceleration, and velocity? Instructions: study the paragraphs and charts below and answer the questions. Speed or Velocity? Speed is the rate of motion, or the rate of change of position. It is expressed as distance moved (d) per unit of time(t). Speed is a scalar quantity with dimensions distance/time. Speed is measured in the same physical units of measurement as velocity, but does not contain an element of direction. Speed is thus the magnitude component of velocity. Velocity contains both the magnitude and direction components. speed = distance/time velocity = displacement / time acceleration Acceleration, (symbol: a) is defined as the rate of change of velocity. It is thus a vector quantity with dimension length/time². In SI units, acceleration is measured in meters/second². To accelerate an object is to change its velocity, which is accomplished by altering either its speed or direction (like in case of uniform circular motion) in relation to time. Acceleration can have positive and negative values. Any time that the sign (+ or -) of the acceleration is the same as the sign of the velocity, the object will speed up. If the signs are opposite, the object will slow down. Acceleration is a vector quantity. When either velocity or direction changes, there is acceleration (or deceleration). To accelerate an object requires the application of a force. An instantaneous acceleration is the change in velocity at one moment. QUESTION: If a car accelerates from 5 m/s to 15 m/s in 2 seconds, what is the car's average acceleration? QUESTION: How long does it take to accelerate an object from rest to 10 m/s if the acceleration was 2 m/s 2? QUESTION: Carl started to run at 10 km/h when he left his house. He arrived at school 30 minutes later. How fast was he running when he arrived there? Assume that his average acceleration was 30 km/h 2.

2 Graphing Velocity and Acceleration A car accelerates from rest. The following two graphs are created using a java applet (see below). The graph of velocity (m/sec.) vs. time (sec.) is a straight line for accelerating objects. acceleration = velocity / time What is the slope of this graph? Please enter your answer in the space provided: meters/second² The graph of distance (x) vs. time (t) is a curve where the equation of motion is: x = 1/2 at². What value of (a) would you expect for this graph? Hint: For each value of t (in s), there is only one value for x (in m). Pick any ordered pair for t and x and substitute them into the above equation. Then solve for a. meters/second²

3 Acceleration Due to Gravity Galileo was the first to find out that all objects falling to Earth have a constant acceleration of 9.80 /s2 regardless of their mass. Acceleration due to gravity is given a symbol g, which equals to 9.80 /s2. Therefore, if you drop a pen, it should behave like this... Time (s) Velocity (m/s) Displacement (m) For all previous equations, we can substitute g for a: QUESTION: How long will it take for an apple falling from a 29.4m-tall tree to hit the ground? s x = 1/2 at² a=2x/t 2 = 1.9 or 2

4 1. The units for acceleration are: Test your Understanding: a) m/sec b) m/sec² c) sec d) (m/sec)² 2. Which of the following are true about acceleration? a) Acceleration is a change in velocity b) An applied force is required for acceleration to occur c) Acceleration can be either + or - in value. d) All of the above 3. In the graph shown above for an accelerating object, the acceleration is closest to? a) 1 meters/second² b) 2 meters/second² c) 3 meters/second² d) 4 meters/second² 4. The units for velocity are: a) m/sec² b) sec. c) miles d) m/sec 5. The slope of the graph of velocity vs. time (x-axis, velocity; y-axis, time) is: a) distance b) acceleration c) speed

5 answers: 1. b 2. d 3. b 4. d 5. b