Presentation on theme: "How fast? Measuring speed. What is speed Speed is the quantity that tells us how fast something is moving. For example: The car’s speed was 50 km per."— Presentation transcript:
What is speed Speed is the quantity that tells us how fast something is moving. For example: The car’s speed was 50 km per hour when it hit the wall. We give its value including the unit, written as km/h. In science, we usually measure speed in metres per second- m/s.
Distance and time How can we measure a runner's speed? We need to find how many metres a runner travels in each second. We measure distance and time, and we calculate Average speed=distance travelled/time taken Or simply Speed=distance/time We have to say average speed because the runner's speed may be changing as they run
You can measure the distance between the two points using a tape measure. You can measure the time taken using a stopwatch. Task: 1. A car travels 100m in 5s. What is its average speed? 2. A red car travels 400m in 20s, a blue car travels 660m in 30 s. Which car has the greater average speed?
Speed check Speed camera may be used to check that drivers are not going too fast. A speed camera stands at the side of the road. It takes a photograph of any car which is speeding. 1.There are two detector strips in the road- distance 2. Camera detects the car, and camera measured the time. And we know the speed- mini computer calculates
Light gates We can use light gates in laboratory. This is similar to speed camera, it measures the speed of moving object. We have two beams, and when the trolley breaks it, it sends the pulse of electricity to the timer. Light gates are useful because they can measure very shot time intervals- less than a second.
Speed calculation Calculate the skidoo’s speed? IT takes about 5 minutes to travel 8 km along the track. Distance travelled=8km=8000m Time taken=5 minutes=300s Speed=distance/time=8000m/300s=26.7m/s
How far? The faster you run and the longer you run for; the farther you will get. Distance travelled=average speed x time taken Example: A bus is traveling along a road. Its speed is 25m/s. How far will it travel in one minute? Distance travelled=25m/s x 60s=1500m
How long? Time taken= distance travelled/average speed Example: An aircraft flies at an average speed of 250m/s. How long will it take to fly between two airports which are 750 km away. Time taken= 750000m/250m/s=3000s
Distance/ time graphs Distance is shown on the y-axis and time on the x- axis 1) If an object is moving at a steady speed, the graph will be a straight line sloping upwards. 2) For two moving objects. If one graph line slopes upwards more steeply, it is because of grater distance in each second. 3) Graph with object which is speeding up.
Distance time graphs Drawing distance/ time graphs Section of journeyTime/ sDistance/ m Start00 A50500 B150900 C200900 D2501000 E3002000