Science - physics test revision
A racing cyclist practices by riding around a track. A student want to find the average speed of the cyclist. Describe a method that the student could use to find the average speed.
- Time how long it takes for the cyclist to go 3 times around the track -Measure how long the track is and multiply it by 3 -Divide the distance over the time and the student will have the answer Use the total time to do the entire course. Divide total distance / total time, that = average speed.
Example: Bob has a spring that is 12 cm long, he hangs a 1N weight from the spring, it extends to 16 cm. Calculate the stiffness of Bob's spring.
1=Kx(16-12) 1=Kx4 k=1/4(n/cm) = 0.25 N/cm
Elastic potential energy
A force acting on an object may cause the shape of an object to change. Elastic objects can store elastic potential energy if they are stretched. For example, this happens when a catapult is used.
Displacement-time graph
A graph with time on the x-axis and displacement on the y-axis, whose gradient is the average velocity. It shows how far an object has moved in relation to a certain point over a certain amount of time
Distance-time graph
A graph with time on the x-axis and distance on the y-axis, that's gradient is the average speed. It shows how far an object has moved in a certain amount of time.
Speed-time graph
A graph with time on the x-axis and speed on the y-axis, whose slope is acceleration and the area under the line is distance. It shows how an object's speed changes over time
What is m?
A property of the object depending on the arrangement of atoms g a property of space varies on the location.
Speed time graph
A speed-time graph tells us how the speed of an object changes over time. The steeper the gradient of the line, the greater the acceleration (a bigger change in speed in the same time). higher=faster speed, if the line is up, it means you're getting faster, acceleration.
The train continues along a straight track from station B to station C. The graph shows how the velocity of the train changes with time during this part of the journey. SEE GRAPH. use this graph to calculate the acceleration of the train, in m/s^2, during the first 100 seconds after it leaves station B.
Acceleration = change in velocity/time 30/100 = 3/10 = 0.3 m/s^2
HOOKE'S LAW GRAPH
Assuming the limit of proportionality (elastic limit) is not exceeded, a graph of force against extension produces a straight line that passes through the origin. The gradient of the line is the spring constant, k. The greater the value of k, the stiffer the spring.
Calculate the average speed of the train and give its unit.
Average speed: 9/15 = 0.6 km/m Unit: km/m
Kate drives a petal powered car up a hill. Energy transformation:
Chemical energy -->kinetic energy-->GPE-->heat and sound energy
Elastic potential energy formula
Elastic potential energy (J) = 0.5 x spring constant (n/m) x extension^2 (m)
Hooke's Law for a spring:
F=kx F=force applied (N) K=spring resistant (stiffness - n/m or n/cm) X=extension of spring (cm/m)
force equation
Force (N) = mass(kg) x acceleration(m/s^2)
Forces and elasticity
Forces may change the shape of an object. An elastic object such as a spring stores elastic potential energy when stretched or squashed. The extension of an elastic object is directly proportional to the force applied.
Energy transformation example: Bob falls off a wall
Gravitational potential energy ---> kinetic energy --> heat/sound energy
*Stretching springs (including how to setup the experiment) : BBC BITESIZE READ
Hooke's law: double force, double extension as well. Spring and stand, clamps down, hung spring from lampstand, got a ruler, one newton, 2 newtons. Plotted a graph, force dependant on independent (x) and extensions (measured) dependent (side axis). Hooke's law says that graph will be straight line. Also, formula: f=kx (f is force, x is extension, k is spring constant) If its a spring that's hard to stretch, it has a big value of K, whereas if you can stretch the spring really easily, it has a small value of k
Distance
How far an object travels or the length between two points. It is a scalar quantity and is found using the equation d=vt
Energy
If an object has energy, it can do stuff
What is energy measured in?
Joules
Work unit:
Joules
Kinetic energy (with formula)
Kinetic energy is the energy of motion. An object that has motion - whether it is vertical or horizontal motion - has kinetic energy. There are many forms of kinetic energy - vibrational (the energy due to vibrational motion), rotational (the energy due to rotational motion), and translational (the energy due to motion from one location to another). To keep matters simple, we will focus upon translational kinetic energy. The amount of translational kinetic energy (from here on, the phrase kinetic energy will refer to translational kinetic energy) that an object has depends upon two variables: the mass (m) of the object and the speed (v) of the object. This equation shows the relationship between kinetic energy (J), mass (kg) and speed (m/s): kinetic energy = 1⁄2 × mass × speed2
GPE (with formula)
Mass of object x gravity x height
Elastic Limit
Maximum force that a spring can take before becoming permanently stretched.
Can energy be created or destroyed?
No, it can only transform into different types
Do rubber bands obey hooke's law
Rubber bands do NOT obey Hooke's Law. Their resistance to extension is NOT linearly proportional to their extension. The resistance of rubber to extension is also a function of how fast the rubber is extended. One way to measure this is to suspend a weight from a rubber band, set the weight into vertical motion of some amplitude, and measure the period of the resulting damped oscillation as a function of its amplitude. To accurately model the rate-dependent motion, the use of non-linear differential equations is required.
Velocity in a direction
Speed on side axis time on bottom. If the speed axis can go negative, we call it a velocity time graph.
The spring constant
The spring constant k is different for different objects and materials. It is found by carrying out an experiment. For example, the unloaded length of a spring is measured. Different numbers of slotted masses are added to the spring and its new length measured each time. The extension is the new length minus the unloaded length.
Displacement
The straight-line distance between the start and end points. It is a vector quantity
the maximum speed of the train must be higher than the value you have calculated. Explain why.
The train accelerates from standing still at station A and accelerates to standing still at station B. The maximum speed of the train is its terminal velocity which is faster than the time it's slowing down (accelerates) and accelerates. DRAW GRAPH
Different types of energy
Thermal energy (hot things) Kinetic energy (moving things) Potential energy (gravitational - high up things) Elastic (stretched things) Electrical energy Sound Light (electromagnetic energy)
Hooks law
When an elastic object - such as a spring - is stretched, the increased length is called its extension. The extension of an elastic object is directly proportional to the force applied to it: F = k × e F is the force in newtons, N k is the 'spring constant' in newtons per metre, N/m e is the extension in metres, m This equation works as long as the elastic limit (the limit of proportionality) is not exceeded. If a spring is stretched too much, for example, it will not return to its original length when the load is removed. Script: Elastic objects (such as a spring) can store elastic potential energy when they are stretched. For example this happens when a catapult is stretched back. When an elastic object -- such as a spring -- is stretched, the increased length is called an extension. The extension of a truly elastic object (again, such as a spring) is directly proportional to the force applied, provided the limit of proportionality is not exceeded. Meaning the object being stretched doesn't become permanently deformed, such as when a spring doesn't return to its original position after the load is removed. This proportionality is called Hooke's Law and the Force is equal to the spring constant times the extension. The spring constant is measured in N/m and is different for different objects and materials. You work it out by carrying out an experiment with an elastic object and adding a load or force to it. You then measure the extension of the spring and sub the numbers into the formula to get the spring constant. The greater the value of k, the stiffer the spring.
Power (with formula)
Work done/time taken
Gravity is...
a force that pulls all masses
Work done is...
amount of energy transfered
Acceleration
change in speed/time Any change in the speed or direction of an object, measured in m/s/s
Acceleration equation and unit
change in speed/time taken unit: m/s2
Displacement
distance in a direction
displacement
distance in a direction (3 N)
What does h stand for in GPE formula
distance raised against gravitational force (m)
Distance time graph:
distance side axis against time bottom axis. If the line is going down, you're going back towards the start Note that the steeper the line, the greater the speed of the object. The blue line is steeper than the red line because it represents an object moving faster than the object represented by the red line. The red lines on the graph represent a typical journey where an object returns to the start again. Notice that the line representing the return journey slopes downwards. Changes in distances in one direction are positive, and negative in the other direction. If you walk 10m away from me, that can be written as +10m; if you walk 3m towards me, that can be written as -3 m. Background information The vertical axis of a distance-time graph is the distance travelled from the start, and the horizontal axis is the time taken from the start. Features of the graphs When an object is stationary, the line on the graph is horizontal. When an object is moving at a steady speed, the line on the graph is straight, but sloped. The diagram shows some typical lines on a distance-time graph.
Speed:
distance/time
Irregular objects displacement method
drop it in water, see how much the water rises (displacement cm) water density is Liters. Everything under will float, some float underwater more since the object takes space that water occupied makes it raise a force a push or a pull measured in N. they make things accelerate or change objects shape. density = mass (object's weight)/volume (displacement)
acceleration formula
final velocity - initial velocity / time
If the earths gravitation is 9.8
gravitational field = object field
What does g stand for in GPE formula
gravitational strength (in N/kg)
motion
how far apart 2 things are
distance
how far apart things are (3 m)
Speed
how fast something is traveling (m/s)
Volume
length x width x height
Density
mass/volume Density = g Measured in g/cm^3 or hg/cm^2
Density (including how to measure density):
mass/volume Nucleus super dense because big mass but very small volume. Length x width x height = volume. Density is the mass per unit volume. This means that the density of any solid, liquid or gas can be found by dividing its mass in kilograms by its volume in cubic metres. Density can be found using the equation: Density = {mass \over volume} P = {m \over v} The unit for density is kg m-3 The density of water is approximately 1000 kg m-3 and air is approximately 1.3 kg m-3
extension
original length - the length of the object after straight line extends with same amount . measured in N/cm
plastic
put force and it wont come back
Elastic rubber band:
put force, release and it will come back
Rubberbands don't follow hook's law
put in numbers to it and solve it that will prove it
Velocity
speed in a direction (3 m/s to north)
A train travels 9km from station A to station B. It takes 15 minuets. State the equation linking average speed, distance moved, and time taken
speed=distance(m)/time(s)
Weight/forces:
the force of gravity pulling down on masses. On earth every kilogram of mass, weighs ten newtons. On the moon, the weight would be lower. Gravity is a force that attracts objects with mass towards each other. The weight of an object is the force acting on it due to gravity. The gravitational field strength of the Earth is 10 N/kg. The stopping distance of a car depends on two things: the thinking distance and the braking distance. Weight Weight is not the same as mass. Mass is a measure of how much stuff is in an object. Weight is a force acting on that stuff. You have to be careful. In physics, the term weight has a specific meaning, and is measured in newtons. Mass is measured in kilograms. The mass of a given object is the same everywhere, but its weight can change. Gravitational field strength Weight is the result of gravity. The gravitational field strength of the Earth is 10 N/kg (ten newtons per kilogram). This means an object with a mass of 1kg would be attracted towards the centre of the Earth by a force of 10N. We feel forces like this as weight. You would weigh less on the Moon because the gravitational field strength of the Moon is one-sixth of that of the Earth. But note that your mass would stay the same. Weight On Earth, if you drop an object it accelerates towards the centre of the planet. You can calculate the weight of an object using this equation: weight (N) = mass (kg) × gravitational field strength (N/kg)
Equation for work
w=fd work done=force applied x distance (meters) through which is applied
Power unit
watts
weight (N)
weight (N) = mass (kg) × gravitational field strength (N/kg)
How much would the same person weigh on the Moon, if the gravitational field strength is 1.6N/kg?
weight = mass × gravitational field strength weight = 60kg × 1.6 N/kg weight = 96N
A person has a mass of 60kg. How much do they weigh on Earth, if the gravitational field strength is 10N/kg?
weight = mass × gravitational field strength weight = 60kg × 10N/kg weight = 600N
Calculate the length of the spring when 1.5 N is hung from it
x=f/k = 1.5/.25 = 6 cm 12+6= 18 cm
