Physics 5 Flashcards
What force us created when a object is pulled along the ground?
Friction
How can friction be reduced
- Using rollers or wheels
- Having a smooth surface
What are the types of forces
- friction
- weight (gravity)
- upthrust
- magnetic
- electrostatic
- nuclear
- thrust
In what unit are forces measured
N -> newtons
Air resistance and water resistance are forms of….
Drag
When does the drag force increase?
When speed increases
Top speed
The maximum speed a object can go
Energy stores
- kinetic
- chemical
- thermal
- gravitational potential
- elastic potential
- sound
Law of conservation of energy
Energy is never created or destroyed only transferred or stored
Equation of speed
Speed= distance
—————–
time
Mean (average) speed
total distance
———————
total time taken
steep line on distance-time graphs
Means you are travelling quickly
Horizontal line on distance-time graph
Not moving at all
Relative speed
Add= if you are on a train and the train is moving at 50km/h and you move the same direction at 3km/h your relative speed is 53km/h
Subtract= if you are on a train which is moving at 50km/h and you move in the opposite direction at 3km/h your relative speed is 47km/h
Multiply=if two trains are traveling at 50km/h towards each other the are moving at a relative speed of 100km/h
Moment equation
Moment of the force = force x perpendicular distance from pivot
(N m) (N) (m)
Lever
A lever is a long bar that turns around the pivot
Pivot
The point where the object turns
Synonym for pivot
Fulcrum
Rule to move load
The longer the lever the easier it is to move the load
What does the lever do
Acts like a force multiplier if the effort distance is larger than the load distance
In equilibrium
When the forces are balanced
What are most machines used for
Use smaller force to move a object
Name 3 simple machines
- lever
- ramp
- pulley
Why are Ramos efficient
It needs less force to push a object up a ramp than it does to lift it directly
When is Less force needed in a ramp
The shallower the slope the less force needed, but more distance to reach its height.
Pulley rule
If the force is halved the distance the rope is has to be double
What does work mean
The amount of energy transferred when a force moves something
Formula to calculate work
Work done = force x distance moved
J) (N) (m
What is a force field
A force field is a space where a non-contact force has a effect
What are magnetic fields
The space around a magnet where it can attract magnetic materials
How can you find the shape of a magnetic fiel
Using iron fillings
Which objects have a gravitational field
All objects with a mass have a gravitational field
What happens when objects are in each other’s gravitational field.
They attract each other
What is the earths gravity
~ 10N/kg
Equation for weight
Weight (N) = mass (kg) x g (N/kg)
What kind of forces are there
- magnetic fields
- gravitational fields
When can static electricity build up?
When two different materials rub together
What do atoms consist of
- a central nucleus with small particles called electrons moving around it.
- the nucleus has a positive charge and each electron has a negative charge.
- this way they are balanced
- the total positive and negative charges are usually the same.
What happens when you rub two insulating materials together
Some electrons may be transferred from one object to the other
Can the positive charges be tranfered
Because they are fixed to the nuclei of the atom
What happens to the object that ends up with more electrons
It has a overall positive charge
What happens when you rub a acetate rod with a piece of cloth
The acetate ends up with less negative electrons and has a overall positive charge, and the cloth has a overall negative charge.
What happens when you rub a polythene rod with a piece of cloth
The negative electrons from the cloth move to the rod making the rod negative and the cloth positive.
What can attract uncharged objects
Something with a charge of static electricity, it’s very small normally just notice it with small things (e.g hair)
What is the electric field
The space around a charged object.
When is the field stronger
When it’s closer to the object
What is a electric current
The flow of electrons, which are negatively charged particles
Series circuit: does the current vary?
No
Series circuit: do all the bulbs go off when a switch is opened
Yes
Series circuit: If you add more bulb to the circuit what will happen
The current is reduced and the bulbs get dimmer
Parallel circuit: is the current always the same
The current separates throughout the circuit because of junctions
Parallel circuit: how are the bulbs controlled
Each bulb is controlled individually (depending where the switch is placed)
Parallel circuit: what happens if you add more bulbs
The bulbs all stay at their original brightness, the current trough each bulb stays the same.
How do we measure current
With a ammeter (amps)
How do we measure the voltage
Using a voltmeter (volts)
What is resistance
A way of saying how easy or difficult it is for the current to flow through it.
Factors that affect resistance
- the longer the wire the higher the resistance
- the thicker the wire the higher the resistance
- insulators have a very high resistance
What are the units for for resistance
ohms
How do you calculate voltage
Voltage (V)= current (A) x resistance (ohms)
What is a electromagnet
A wire with a electric current flowing that has a magnetic field
How do you increase the strength of a electro magnet
- increasing the number of coils around the wire.
- increasing the current in the wire.
- using a magnetic material as a ‘core’ inside the coil of wire.
When does the direction of the magnetic change
When the current changes direction
