Forces - Types of forces
- Balanced Forces act in pairs to produce no resultant acting on the body.
- Unbalanced Forces act in pairs to produce a resultant force acting on the body and in the direction of the resultant force.
- Massis the amount of material within a body.
- Weight is the force that acts on a body due to its mass in a gravitational field
- Static Friction is the force that prevents a body from sliding along a material.
- Frictionacts to oppose movement and therefore always acts in the opposite direction to the movement and can generate heat energy
- Air Resistanceis a type of resistance
- Pressure is the force acting per unit area (measured in Newtons per metre squared, N/m2 OR Pascals, P)
"The extension of a spring/material is directly proportional to the applied load, provided the elastic limit is not exceeded"
Newton's 1st Law
"A body will remain at rest or in uniform motion unless acted upon by an external force"
Newton's 3rd Law
"If Body A exerts a force on Body B, then Body B will exert a force on Body A that is equal in magnitude and opposite on direction"
Speed is a scalar (magnitude only)
Speed (m/s) = distance (m) / time taken (s)
Velocity is a vector (magnitude and direction)
Velocity (m/s) = displacement (m) / time taken (s)
- Charge can be positive or negative
- Measured in Coulombs (C)
- Opposite charged objects attract
- Like charged objects repel
- When charge flows we call this a current
- An electric current is a flow electrons which are carrying negative.
Where is it / When does it occur?
- Lightning - negatively charged particles sink to the bottom of the cloud. When the positive and negative charges grow large enough, a giant spark occurs
- Electric Shocks - The static electricity is formed when we accumulate extra electrons (negatively-charged particles which we rub off carpeting) and they are discharged onto the doorknob.
- Photocopier -
- a copying plate is electrically charged;
- an image of the page you want to copy is projected on to the plate;
- where light falls on the plate, the electrical charge leaks away;
- the parts of the plate that are still charged attract bits of black powder;
- the black powder is transferred from the plate to a sheet of paper;
- the paper is heated to melt the toner and therefore make the black powder stick permanently to it
- there is now a copy of the original page.
Static Electricity - The Dangers
- Explosions - There are inflammable gases or vapours or a high concentration of oxygen. A spark could ignite the gases and cause an explosion.
- Electric Shocks - You touch something with a large electric charge on it. The charge will flow through your body causing an electric shock. This could cause burns or even stop your heart. A person could die from an electric shock.
Cloth & Rod
- Positively charged cloth is rubbed against a rod
- Positive electrons are transferred onto the rod
- If 2 positively charged rods come together, they will repel each other
Circuits and Current
- For electricity to flow there must be an energy source (cell, battery, power pack) and a complete conducting loop (complete circuit).
- Materials that allow electricity to pass through them are called conductors and materials that do not normally allow electricity to flow through them are called insulators.
- Current- the charge passing through a point in the circuit per second.
- Current is measured with an ammeter and is measured in Amps (A).
- Resistors oppose the flow of electricity and the unit for resistance is Ohms (Omega symbol)
- A series section in a circuit has one path and a parallel section in a circuit has more than 1 path
- Bulbs in parallel are brighter than bulbs in series
- This can be explained in terms of the energy avaliable from cell or battery being fully avaliable to each bulb in parallel, but shared by bulbs in series.
- When a single path splits into two paths the current in each path will be the same if the resistance in each path is the same. If the resistance in each path is not the same, the path with the least resistance will have the greatest current.
- Iron, steel, nickel and cobalt are the only magnetic materials.
- A permanent has a magnetic field around it.
- A magnetic field is an area around a magnet where magnetic materials experience a force
- The poles at each end of a magnet are called North and South.
- The field lines flow from the North Pole to the South Pole.
- Opposite (unlike) poles attract, and like poles repel.
- When a currenct flows in a wire there is a small magnetic field produced around the wire.
- An electromagnet consists of a coil carrying a current around an iron or steel core
- The strength of an electromagnet is controlled by the number of turns in the coil
- Electromagnets are commonly used in:
- Hard Drives
- Scrap Yards
- MRI Scanners
- Some advantages of Electromagnets (over permanent magnets) are:
- On scrap yards, the magnetic fields can be switched on and off, so material can be easily disposed of.
- The strength of the magnetic field can be changed.
- Some disadvantages of Electromagnets (over permanent magnets) are:
- They are environmentally friendly
- They require no power source
- Always maintain a magnetic field.