Let’s get the common misconception out of the way first: moving objects do not remain in motion because there is a force that keeps them going. In fact, it’s the opposite. Moving objects always remain in the same state of motion unless an external force stops them. By “the same state of motion” we mean … Continue reading Forces and Motion
Acceleration and Distance
To find acceleration without measuring time, we can use a combination of the object's mean speed and distance-moved as a substitute for time. We already know that speed is calculated as distance divided by time, so we can rearrange this equation to calculate time as distance divided by speed. Of course, the speed of an … Continue reading Acceleration and Distance
Calculating Acceleration
Acceleration is the rate of change of speed (we will leave aside velocity for now) and that means we can calculate acceleration if we know the speed of an object at two different times. The object’s acceleration is given by its change in speed, divided by the time interval. Positive acceleration indicates that the object … Continue reading Calculating Acceleration
Measuring Speed
This is the third part of a mini-series looking at motion and here we’ll be considering different ways to measure speed as well as some common sources of error. In theory, speed is easy; we just need a distance (measured using a ruler, for example) and a time (probably measured using a stopwatch but ideally … Continue reading Measuring Speed
Speed and Acceleration
When a stationary object starts moving in a straight line, its motion can be divided into two stages. The first stage is when the speed of the object is increasing; the second stage is when the object has reached a steady speed. We can rephrase these two stages using the word acceleration; the first stage … Continue reading Speed and Acceleration
Speed and Velocity
In many situations, the word “speed” is used when in fact “velocity” would sometimes be more appropriate. Speed is the rate of change of distance: the word “rate” indicates time, so speed is simply a measure of how much the distance changes in each second of movement. If you took 80 seconds to run 400 … Continue reading Speed and Velocity
Heisenberg and Sheldon; speed and uncertainty
In my very last Y11 lesson of last term I did a 15-minute dash through some of the weirder bits of physics, including Heisenberg's uncertainty principle. This says that, for example, you cannot know the exact values of an object's position and speed (actually its momentum). More excitingly, you cannot know the exact energy of … Continue reading Heisenberg and Sheldon; speed and uncertainty
Squirrel speed
How fast can a squirrel run? I'm talking here about a red squirrel (the type we have in Jersey) and I'm assuming that the creature has been startled and is dashing for cover. Think for a moment: what sort of experiment could you arrange to answer this question? At its simplest, this is a time-and-distance … Continue reading Squirrel speed
Flight facts
How long do you think it takes to get to cruising altitude on a long-haul flight? Aircraft travel has become so smooth that you could be forgiven for thinking that within 20 minutes, at the most, you're in level flight. And you would probably also think that the aircraft's speed is fairly constant from about … Continue reading Flight facts
Power is the Rate of Change of Energy
There are two booklets available on physbang.com to help you revise the equations that you are expected to know by the end of Y10. These booklets were posted a few months ago (click here to read that post and download the booklets) but it has since been pointed out that one equation is missing: sorry … Continue reading Power is the Rate of Change of Energy
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