Speed is the distance that something moves in a given time.
20 metres per second means that something moves 20 metres in one second.
What about 50 miles per hour? Or 600 kilometers per minute? - They're all speeds.
In school we use metres per second
Experiment: How to display speeds
Using a datalogger draw graphs of distance against time for...
1) Acceleration, 2) Constant Speed, 3) Rest, 4) Deceleration.
Save each of these graphs, and then import them into a single word document. Next to each graph, describe what you see.
How to interpret distance time graphs
Task: work through the online exercises
Complete the worksheets on Speed and Acceleration
Physics for You pp134
Task: Define the following terms: Distance, Time, Speed, Acceleration
What does the distance graph of an accelerating object look like?
We need to define some new ideas before we can work with this.
Vectors are physical quantities with size and direction. Scalars are quantities with size only.
Displacement: Displacement is distance with direction. Eg: 100m SW
Velocity: Velocity is speed with a direction. Eg: 30m/s NNE.
Acceleration: Because acceleration is a vector it has size and direction.
Speeding up is positive acceleration, slowing down is negative acceleration.
Experiment: Drawing velocity-time graphs with ticker tapes to show acceleration.
So we can use distance time graphs to show velocity and velocity time graphs to show acceleration.
Challenge: Can you work out how to find the distance travelled from a velocity-time graph?
Extension: Playing with s-t, v-t and a-t graphs
Physics for You pp130-133
What is a force? Can you name 5 different forces?
How do forces affect motion?
So how do things move if there are no forces acting on them?
What will happen to the box when the following forces are applied?
Newton's Laws of Motion tell us about the way objects behave when forces act.
"Every body continues at rest or constant speed in a straight line unless acted upon by an external force."
Explain these using Newton's 1st Law:
"The resultant force on an object is equal to the objects mass times its acceleration"
Work through the online exercise to explain how Newton's 2nd Law allows us to do this...
If an unbalanced force acts on a body then it experiences an acceleration.
The acceleration is related to the unbalanced force by Newton's 2nd Law.
Experiment: How is the force on the trolley related to it's acceleration?
Complete the worksheets on Forces
Physics for You pp 139 q14-17 and pp153 q37 and 38
There are two types of friction:
Air resistance is the bouncing of air molecules off the side of a barrier. The faster something is moving, the more molecules bounce off it every second, so the bigger the force of air resistance.
Task: Draw a diagram to illustrate this
When an object falls it accelerates because of the force of gravity.
As its speed increases the force of air resistance pushing upwards also increases.
When the upward force of air resistance is equal to the downward force of weight, then the object will stop accelerating and fall with constant speed. This is called Terminal Velocity .
Watch film and record the speed of a parachutist at different times in her descent.
Plot the speed-time graph for the parachutist and label it to show the different parts of the descent.
More on speed-time graphs
Using the simulation experiment to answer these questions:
Look at Physics for you pp98 for help with this.
Physics for You pp98
You have an unknown mass, a 20g mass, a pivot and a metre ruler.
Find the unknown mass.
So what do you remember about moments?
and they are calculated from...
1. Work through the online experiment, and construct a table showing the clockwise and anticlockwise moments for 10 different situations.
NB: Make sure the spring balance vertical, beam horizontal box is ticked.
2. Now repeat the experiment for real, and draw a second table.
3. Compare the results for both of the experiments.
Complete the worksheet on Balancing
Physics for You pp100-101
When forces are applied to materials, they deform. Hooke's Law describes how materials behave when the are deformed.
What is the difference between length and extension?
What do we mean by the term elastic deformation?
What is the elastic limit?
We write an equation for a straight line graph like this, as...
y a x
In this experiment, y= F, and x= e,
F a e
F = ke
Where k is a constant that relates Force to extension, which is called the spring constant. The gradient of our graph tells us this.
k changes from one material to another.
Do the same experiment, but this time to destruction with an elastic band.
Draw a diagram, and complete the table of results for your experiment
What do you notice about the graph?
Mark on your graph the following features...
Now work out the spring constant (N/cm) for the elastic band during the elastic part of the deformation.
Extension: Demo of Hooke's Law applied to stretchig a wire.
Complete these problems using the ideas of Hooke's Law.
Complete the worksheet on changing shape
Physics for You pp79