34 experiments found
Clear filtersA bulb glows only when the circuit is closed: an unbroken loop from the cell, through the bulb and back
Open up a torch and switch it on and off. Loosen a wire, add a second cell and try a broken bulb, and find out when current can flow and the bulb glows.
An object is at rest if it does not change its position compared with what is around it, and moving if it does; so rest and motion depend on what we compare with
Watch a passenger in a school bus, first from the roadside and then from a seat in the bus. Is the passenger moving? Is the tree? Find out why the answer depends on where you watch from.
At a mirror, the angle of reflection equals the angle of incidence
Shine a ray of light at a plane mirror at different angles, measure the angle of reflection, and compare a mirror with a rough surface.
Light travels in straight lines, so an opaque object blocks it and casts a shadow that grows as the light comes closer
Move a torch closer to and further from an object and watch its shadow on a screen grow and shrink. Try opaque, translucent and transparent objects.
Transparent materials let almost all light through, translucent materials let some through, and opaque materials let none through and cast shadows
Shine a torch through different materials, see how much light passes, and sort them into transparent, translucent and opaque.
Magnets attract iron, steel, nickel and cobalt; most other materials, including most metals, are non-magnetic
Test everyday objects with a magnet, find out what they are made of, and sort them into magnetic and non-magnetic materials.
Denser liquids sink below less dense liquids
Pour honey, dish soap, water and oil into a cylinder and watch them stack in layers by density.
Mass is the amount of matter and stays the same everywhere; weight is the pull of gravity and changes from place to place
Weigh objects with a beam balance and a spring balance on Earth, the Moon, Mars and Jupiter, and see which reading changes.
Read a ruler from the zero mark to the nearest millimetre, and subtract the starting mark if you cannot start at zero
Measure a pencil, an eraser and a leaf to the nearest millimetre, then learn to measure correctly with a ruler whose end is worn.
Read the bottom of the meniscus with your eye level with it
Read the volume of three liquids in a measuring cylinder at the bottom of the meniscus, and see why your eye must be level with it.
An object sunk in water pushes aside (displaces) its own volume of water
Lower a stone, a key, a marble and a toy into water and measure how much the water rises. Use an overflow can for a stone too big for the cylinder.
In a fair test we change only one thing (the variable we are testing) and keep everything else the same, so we know what caused the difference
Dip paper towels and a cloth in water and measure how much each soaks up. First see how an unfair test can fool you, then make it fair by changing only one thing at a time.
A lever balances when the clockwise and anticlockwise moments are equal
Hang a load on a metre-rule lever, push down on the other side, and find every way to balance it.
A ramp is a simple machine: a longer ramp needs a smaller push, but you push the load a longer way
Load a sack of rice onto a truck. Lift it straight up, then push it up ramps of different lengths, on a trolley or dragged, and see how much push each one needs.
Simple machines (lever, pulley, wheel and axle, inclined plane, wedge, screw) make work easier by changing the size or direction of a force
Look at how everyday tools and devices work, including a dhiki and a janto, and sort them into the six types of simple machine.
Sound is made when something vibrates; the faster it vibrates, the higher the note (pitch)
Blow across the top of a bottle and tap it with a spoon, with more and more water inside. Find what vibrates each time, and how the water changes the note.
A battery's capacity in mAh is the charge it holds: hours to charge = capacity ÷ charger current (plus about 20% losses), and energy in Wh = capacity (Ah) × voltage
Pick a phone battery of 3000, 4000 or 5000 mAh and a 1 A, 2 A or 3 A charger. Work out how long it takes to charge from empty, how much energy it stores and how many hours the screen can stay on.
An LED takes a fixed forward voltage (about 2 V for red, 3.2 V for blue and white); a resistor in series takes the rest, so by Ohm's law R = (supply − LED voltage) ÷ current
Light a red, green, blue or white LED from a 5 V, 9 V or 12 V supply. Work out the resistor that lets just the right current flow, and how much power the resistor turns into heat.
Energy = power × time: a 0.4 kW panel in 5 hours of sun gives about 0.4 × 5 × 0.8 = 1.6 kWh, after the losses of heat, dust and wiring
Put 2 to 10 solar panels on a roof and choose how many sunny hours a day it gets. See how many kilowatt-hours they make a day and a month, how many LED bulbs that lights for an evening, and how much CO₂ it saves against coal power.
Magnitude is a logarithmic scale: each step of 1 means 10 times the shaking on a seismograph and about 32 times (10^1.5) the energy
Pick two earthquakes by their magnitude, from a small 3 to a great 8, and see how many times more the ground shakes and how many times more energy the bigger one lets out. Find why the 7.8 Gorkha earthquake of 2015 was so much worse than a 5.
Gravity pulls a satellite towards the Earth and keeps it moving in a circle; in an orbit of radius r its speed is v = √(GM ÷ r), so higher satellites move slower and take longer to go round
Put a satellite in a low orbit like the International Space Station, in a GPS orbit, or in a geostationary orbit used for TV. See how far it is from the Earth's centre, how fast gravity makes it go and how long one trip round the Earth takes.
Light travels at about 299 792 km every second, so the time it takes is distance ÷ speed: a fraction of a second from a satellite, 8 minutes from the Sun and more than 4 years from the nearest star
Send light to us from a GPS satellite, the Moon, the Sun, Mars and the nearest star, and work out how long each journey takes. Find out why we see the Sun as it was eight minutes ago.
Light travels in straight lines, so a stick's shadow is its height ÷ tan(the sun's height): the lower the sun, the longer the shadow, and with the sun straight overhead there is no shadow at all
Stand a stick in the sun and move the sun from low in the morning sky to straight overhead. See how long the shadow is each time, and why shadows are long in the morning and evening and shortest at noon.
A scale model divides every size and distance by the same number: if the Earth were a 22 cm football, the Moon would be a 6 cm ball 6.6 m away and the Sun a 24 m ball 2.6 km away, so space is mostly empty
Shrink the Earth to a football, a cricket ball or a marble, and shrink everything else by the same scale. See how big the Moon and the Sun would be, and how far away they would sit.
Force = pressure difference × area: a fan that lowers the pressure under a car presses it onto the road
Switch on a fan that sucks the air out from under a sports car, and see how a small pressure difference over the car's floor gives a huge downforce, more grip and faster cornering. Then blow air in to make the car float, and fire thrusters to see when thrust beats weight and the car flies.
A stretched band stores elastic potential energy E = ½kx²; on release it becomes kinetic energy ½mv², so v = √(2E ÷ m), and at 45° the pellet flies about v² ÷ g: twice the stretch gives four times the energy and twice the speed
Stretch a rubber band and fire a paper pellet. Change the band, how far you stretch it and the pellet's mass, and see the energy stored in the band, the launch speed and how far the pellet flies.
A falling object speeds up until air drag equals its weight; then it falls at a steady (terminal) speed v = √(2mg ÷ (ρCA)), so a bigger canopy falls slower
Hang a 20 g, 50 g or 100 g toy under a canopy of 0.1 to 1 m², and find how fast it falls once air drag balances its weight, and how long it takes to drop 10 m.
Gear ratio = front teeth ÷ rear teeth: the back wheel turns that many times for each turn of the pedals, so a big ratio goes far and fast but is hard to push, and a small ratio is easy to push but slow
Change the front and rear gears of a bicycle and see how far one turn of the pedals takes you, and how fast you go at the same pedalling. Find the easy gear for a hill and the fast gear for a flat road.
Radioactive atoms decay at random, but in each half-life half of those left decay: after n half-lives 100% × (½)ⁿ remain, whether the half-life is hours or thousands of years
Watch a crowd of radioactive atoms decay. Choose an isotope used in hospitals or for dating old bones, let half-lives go by, and see what share of the atoms is left and how long that took.
Light arrives almost at once but sound travels only about 343 m a second, so the distance to lightning in km is the seconds from flash to thunder × 0.343
Count the seconds between a lightning flash and its thunder, and work out how far away the lightning struck. Find out why a short gap means you must go indoors at once.
Loudness is measured in decibels (dB): every 10 dB is ten times the sound energy; the level falls about 6 dB each time the distance doubles, and above 85 dB the safe listening time halves for every 3 dB more
Stand near a whisper, a conversation, busy traffic, a pressure horn or a firecracker. See the sound level in decibels, how it drops as you move away, and how long your ears can safely take it each day.
Hot things cool faster the hotter they are than the room: T = room + (start − room) × e^(−kt); a lid and a vacuum flask cut heat loss, giving a much smaller k
Pour tea at 90 °C into an open cup, a covered cup or a vacuum flask in a 25 °C room, and follow its temperature for an hour to see which keeps it hot and why.
Stopping distance = thinking distance (speed × reaction time) + braking distance (v² ÷ 2μg): doubling the speed doubles the first but four-times the second
A child steps onto the road 30 m ahead. Change the vehicle's speed, the driver's reaction time and the road, and find the thinking distance, the braking distance and whether it stops in time.
A scale shows how hard it pushes up on you: N = m(g + a), so you seem heavier when the lift speeds up upward, lighter when it speeds up downward, and weightless in free fall
Stand on a bathroom scale in a lift. See what it reads as the lift starts going up, moves steadily, starts going down, and, if the cable snapped, falls freely.