Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
5 Cards in this Set
- Front
- Back
|
How can energy be transferred? |
When a system changes, energy is transferred. A system is anything, a single object or a group of objects. When a system changes, some energy is dissipated and stored in less useful ways. The efficiency is the proportion of the total energy supplied that is useful. Can be transferred by: HEATING: eg a pan of water is heated. Energy is transferred into the system by heating to the thermal energy stored of pan and water, which increases temp. DOING WORK: eg a box is lifted up off floor. As lifted, work is done against gravity. Causes energy to be transferred to the box’s kinetic and gravitational potential energy stored. ELECTRICAL EQUIPMENT: electrical devices work by transferring energy between different energy stores. Eg electric irons transfer energy electrically from the mains power supply to the thermal energy store of their metal plates. |
|
|
Work done and power |
If a force moves and object, work is done. Force is needed to make something move, and the thing applying the force needs a source of energy. The force does work to move the object and energy is transferred mechanically from one store to another. Even if energy is transferred usefully or is wasted, it’s still work done. E=FD Power is how much work done per second, the rate of energy transfer. P=E/T |
|
|
What are forces and how do you show them? |
A force is a vector- it has notched size and direction. It is a push or pull on an object that is caused by it interacting with something. Objects may or may not need to be touching (interacting fields). Whenever 2 objects interact, both objects feel and equal but opposite force (Newton’s 3rd law). The pair of forces is called an interaction pair. Free body diagrams show all forces on an object. Shows all forces acting on body, the size of arrows show the relative magnitude of force and the direction. A resultant force is the overall force on a point of object. Objects in equilibrium have a resultant force of 0- they are stationary or moving at a steady speed. |
|
|
Forces and vector diagrams. |
How to use scale drawings to fin resultant force. Draw all the forces acting on an object to scale, tip to take. Then draw straight line from start of first force to end of last force, this is resultant force. Measure length to find magnitude. If all forces add up to a resultant force of 0 its in equilibrium. On a scale drawing, this means that the tip of the last force you draw should end where the tail of the first force you drew begins. If given forces on an object in equilibrium and find missing force, draw our forces you do know, tip to tail, then join end force to start of beginning force. You can also split a force into easier angles, acting together these forces have same effect as single force. |
|
|
What are moments, and how do you make work easier? |
A force, or several forces, can cause an object to rotate. The turning effect of a force is called its moment MOMENT OF A FORCE (Nm) = FORCE X DISTANCE. Distance is the distance normal to the direction of the force. To get maximum moment you need to push at right angles to the spanner. Pushing at any other angle means a smaller moment and so a smaller moment. Leavers make it easier to do work as they increase the distance from the pivot at which a force is applied- the longer the lever, the smaller the force needed to give the same moment. Gears transmit turning effect, as their teeth interlock so that turning one causes another to turn in opposite direction. Transmit rotational effect from one place to another. Use ratios of teeth to work out how many turns it takes to turn another gear. |
