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== Expectations at Key Stage 2 == | == Expectations at Key Stage 2 == | ||
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== The distinction between ‘power’ and ‘energy’ == | == The distinction between ‘power’ and ‘energy’ == | ||
{| class="wikitable" | |||
|- | |||
| [[File:Hare_running-8255.jpg|200px]]|| 10s [[File:800px-Arrow_east.svg.png|35px]]100m | |||
|- | |||
| 30n[[File:242px-Arrow south.svg.png|15px]]|| Energy: 30n x 100m = 3000j<br />Power: 3000j/10s = 300j/s | |||
|- | |||
| [[File:Turtle-8917.jpg|150px]]|| 1000s [[File:800px-Arrow_east.svg.png|35px]]100m | |||
|- | |||
| 30n[[File:242px-Arrow south.svg.png|15px]]|| Energy: 30n x 100m = 3000j<br />Power: 3000j/1000s = 3j/s | |||
|} | |||
The important thing to stress is that in both cases, the ‘work done’ or ENERGY is the same – it being the product of the force (weight of the animal) measured in Newtons, and the distance travelled, measured in meters – regardless of speed. The units for ENERGY are Joules. | |||
POWER is the rate at which the ENERGY is converted. This is measured in Joules per second (Watts). | |||
== Representing Forces == | == Representing Forces == | ||
{| class="wikitable" | |||
|- | |||
| '''Drawing Demand'''|| '''Conceptual Demand''' | |||
|- | |||
| Single Arrow || Single Arrow | |||
|- | |||
| Direction of arrow|| Force has direction | |||
|- | |||
| Straightness of arrow|| Forces act in straight lines | |||
|- | |||
| Length of arrow|| Magnitude of force | |||
|- | |||
| Location of arrow’s tail|| Objects as point masses | |||
|- | |||
|} | |||
<br /> | |||
{| class="wikitable" | |||
|- | |||
| '''Two Arrows'''||'''Two Arrows''' | |||
|- | |||
| Arrows drawn head to head (equal length)|| Balanced forces (zero net force, body being<br />stationary or moving at constant velocity) | |||
|- | |||
| Unequal lengths|| Unbalanced forces | |||
|- | |||
| Arrows drawn in the same direction|| Additive forces in same direction | |||
|- | |||
| Arrows drawn in different directions|| Both forces influence the resultant movement | |||
|} | |||
<br /> | |||
{| class="wikitable" | |||
|- | |||
| '''Multiple Arrows'''|| '''Multiple Arrows''' | |||
|- | |||
| Arrows drawn in various directions to represent all<br />the forces acting on the body|| Direction of individual arrows combined to determine<br />total force; equal and opposite forces cancel one another out.<br />With unequal opposite forces, the net force is the smaller subtracted from the larger. | |||
|} | |||
== Falling Object == | == Falling Object == | ||
{| class="wikitable" | |||
|- | |||
| ||[[File:Arrow-up.jpg|65px]]||[[File:Arrow-up.jpg|65px]] | |||
|- | |||
| [[File:Cylinder3.png|65px]] || [[File:Cylinder3.png|65px]]|| [[File:Cylinder3.png|65px]] | |||
|- | |||
|style="text-align:center"| [[File:242px-Arrow south.svg.png|35px]] | |||
|style="text-align:center"| [[File:242px-Arrow south.svg.png|35px]] | |||
|style="text-align:center"| [[File:242px-Arrow south.svg.png|35px]] | |||
|} | |||
In the first instance, the object is stationary, held in place – with gravity being the only other force acting on it. As it released, the sudden massive imbalance of forces causes the object to accelerate towards the ground. | |||
As it starts to move, it pushes through the air causing air resistance which acts in an opposing direction to the gravity. In the early stage of the descent, the forces are still somewhat unbalanced and while the object does continue to accelerate towards the ground – it does so at a slower rate of acceleration at the start of the fall. | |||
As the object gets faster, air resistance continues to increase, gradually reducing the rate of acceleration until it comes to the point where the upward force of air resistance is the same as the downward force of gravity. At this point the forces are balanced and the object ceases to accelerate. It continues to fall at the velocity (speed) it was travelling when balance point was reached. This is known as the TERMINAL VELOCITY. | |||
== Self-Assessment: Aeroplane == | == Self-Assessment: Aeroplane == | ||
[[File:Force_image_4.jpg|450px]] | |||
Ask | Ask your students to draw the arrows at the point of take-off, mid-flight and as it comes in to land. | ||
== Measuring Forces == | == Measuring Forces == | ||
