Force Demonstrations

See also: Motion

Force is a push or pull that can change the motion or shape of an object. This category introduces the ways forces act, how they are measured, and how they combine. Understanding force provides the basis for explaining motion, stability, and the behaviour of objects in everyday situations.

Demonstration	Materials	Difficulty	Safety	Summary
Air Track Demonstrations	★★★	★★☆	★☆☆	Use a low-friction air track and gliders to demonstrate core kinematics and dynamics ideas including uniform motion, acceleration, momentum, and collisions.
Ballistic Car	★★★	★★☆	★☆☆	The Ballistic Car shows that horizontal motion is unaffected by vertical forces. A spring launcher on a moving cart shoots a ball straight upward; the ball then falls back into the barrel, proving that both cart and ball share the same horizontal velocity.
Balloon Bed of Nails	★☆☆	★★☆	★★☆	A single nail easily pops a balloon because all the pressure is concentrated at one point. But when many nails share the load, the pressure is spread out, allowing a balloon (and by analogy, a person) to withstand much more force before popping.
Bottle Rocket	★★☆	★★☆	★★☆	A plastic soda bottle partially filled with water is pressurized with air using a pump. When released, the escaping air and water propel the bottle upward, demonstrating Newton’s Third Law of Motion and the relationship between force and acceleration.
Dropping Coin and Feather in a Vacuum	★★★	★★☆	★★☆	This demonstration shows that in the absence of air resistance, all objects fall at the same rate. A coin and a feather dropped in a tube filled with air fall at different speeds, but when the tube is evacuated, they fall together.
Force Table Vector Addition	★★★	★★☆	★☆☆	Using a force table with pulleys and hanging masses, students create one or more known forces on a central ring and determine the equilibrant that brings the system to equilibrium.
Gravity Visualized	★☆☆	★★☆	★☆☆	Stretching fabric over a frame to create a “spacetime” surface lets students see how mass curves space and guides motion. By placing heavy and light objects on the fabric and rolling marbles, the class can model orbits, accretion, tides, and even visualize gravitational waves.
Lying on a Bed of Nails	★☆☆	★★☆	★★★	The bed of nails demonstrates how spreading force over a large surface area reduces pressure. A person can safely lie on many nails without injury because the force of their weight is divided among the nails.
Magnetic Force and Separation Distance	★★☆	★★☆	★☆☆	This experiment measures the force between two permanent bar magnets as their separation distance changes. Students collect data and plot graphs to investigate the mathematical relationship, which approximates an inverse square law but may follow a slightly different power law.
Measuring the Gravitational Constant	★★★	★★☆	★☆☆	The Cavendish Experiment, first performed in 1797–98 by Henry Cavendish, measures the tiny gravitational attraction between lead spheres using a torsion balance. From this, the gravitational constant (G) can be determined.
Pascal’s Principle With Syringes	★★☆	★★☆	★★☆	Using syringes connected with tubing, students can demonstrate Pascal’s Principle: when pressure is applied to a confined fluid, the pressure increase is transmitted equally throughout the fluid. This allows a small force applied on a small piston to generate a larger force on a larger piston.
Shoot the Monkey	★★★	★★☆	★★☆	This classic demonstration shows that the horizontal and vertical components of a projectile’s motion are independent. A projectile fired from a cannon hits a monkey that drops from a tree at the same instant, because both fall with the same vertical acceleration due to gravity.
Stomp Rocket	★☆☆	★★☆	★★☆	Students build and launch paper rockets using a plastic bottle, garden hose, and card. By stomping on the bottle, compressed air is forced through the hose, propelling the rocket upwards in a demonstration of Newton’s Third Law.
The Spinning Can	★☆☆	★★☆	★☆☆	A can with small angled holes near its base will spin when filled with water and suspended.
Vacuum Power	★★★	★★☆	★★☆	By attaching a vacuum cleaner to a plywood board with weatherstripping, the suction creates a strong seal against a flat surface. The reduced air pressure between the board and the surface allows normal atmospheric pressure to hold the board firmly in place, demonstrating how pressure and surface area combine to create strong lifting forces.
Balancing a Hammer with a Ruler	★☆☆	★☆☆	★☆☆	A hammer can be balanced on the edge of a ruler (or even another hammer) using rubber bands. The system achieves stable equilibrium because the combined center of mass lies just below the fulcrum.
Balloon Hovercraft	★☆☆	★☆☆	★☆☆	A CD, balloon, and sport drink cap are assembled into a simple hovercraft that demonstrates Newton’s Third Law of Motion and the reduction of friction. Air from the balloon escapes downward through the CD hole, lifting and moving the hovercraft.
Balloon Rocket	★☆☆	★☆☆	★☆☆	A balloon taped to a straw travels along a taut string when released, demonstrating Newton’s Third Law of Motion: the escaping air (action) pushes the balloon forward (reaction). The setup provides a simple model of rocket propulsion.
Block and Tackle with Broomsticks	★☆☆	★☆☆	★☆☆	This demonstration uses two broom handles and a long rope to model a block and tackle pulley system. It shows how increasing the number of rope loops reduces the effort needed to pull two volunteers together, demonstrating mechanical advantage.
Catch a Falling Dollar	★☆☆	★☆☆	★☆☆	This experiment demonstrates human reaction time using a dollar bill. A person tries to catch the bill as it falls, but usually fails because the human reaction time is slower than the time it takes the bill to drop through their fingers.
Center of Gravity Balance Test	★☆☆	★☆☆	★☆☆	Balance on the edge of a curb and test how arm position and the use of short versus long poles affect stability and wobble speed. By changing where mass is distributed, you shift your center of gravity and can measure how that influences balance time.
Centripetal Force Marble	★☆☆	★☆☆	★☆☆	A marble is spun inside a glass. As the marble spins faster, centripetal force from the glass walls keeps it moving in a circular path, temporarily counteracting gravity.
Centripetal Force with Bucket	★☆☆	★☆☆	★☆☆	A bucket of water is swung in a vertical circle without the water spilling out. This demonstrates inertia and the role of centripetal force in circular motion.
Cutting Rope with Rope	★☆☆	★☆☆	★☆☆	This demonstration shows how one piece of rope can be used to cut through another by rapidly sawing back and forth. The heat and abrasion from friction weaken the fibers until the rope snaps. It’s a survival trick that illustrates the physics of friction and energy transfer.
Dollar Bill Inertia Challenge	★☆☆	★☆☆	★★☆	This demonstration uses a dollar bill, coins, and soda bottles to show Newton’s First Law of Motion. When the bill is quickly pulled away, the coins or bottle remain in place due to inertia, as long as friction is minimized.
Dropping Balls From Same Height	★☆☆	★☆☆	★☆☆	This demonstration shows that all objects fall at the same rate under gravity regardless of their mass. Two balls of different sizes dropped at the same time hit the floor together. When one ball is dropped vertically and the other is tossed horizontally from the same height, they still land at the same time.
Finding Centre of Ruler	★☆☆	★☆☆	★☆☆	No matter where you place your fingers under a meter stick, if you slide them together, they will always meet at the stick’s center of gravity. This surprising result shows how friction and weight distribution interact to ensure the balance point is always found.
Floating Ping Pong Ball	★☆☆	★☆☆	★☆☆	A ping pong ball can be suspended in the air stream of a hair dryer. This demonstrates Bernoulli’s principle, which explains how differences in air pressure keep the ball floating and stable in the moving air.
Friction of a Block on an Inclined Plane	★☆☆	★☆☆	★☆☆	A block is placed on a flat board that can be tilted to form an inclined plane. As the incline is raised, the block remains at rest until the downhill pull of gravity overcomes static friction, at which point it begins to slide. The angle at which sliding begins can be used to measure the coefficient of static friction, while constant-speed sliding demonstrates kinetic friction.
Genie in the Bottle Rope Trick	★★☆	★☆☆	★☆☆	A hidden ball inside a bottle creates friction against a rope, making it appear that the rope is magically suspended in the bottle. This trick demonstrates how frictional forces resist motion between surfaces.
Happy and Sad Balls	★★★	★☆☆	★☆☆	This demonstration compares how different materials affect energy transfer in collisions. A "happy" ball made of neoprene rubber bounces high, showing an elastic collision, while a "sad" ball made of norbornene barely bounces, showing an inelastic collision.
Inertia - Which String Breaks	★★☆	★☆☆	★☆☆	A heavy mass suspended by a top string has a string hanging from the bottom. A quick pull on the lower string causes it to snap due to the ball’s inertia, while a slow pull causes the top string to break because it the gravity of the mass add to the force.
Inseparable Books	★☆☆	★☆☆	★☆☆	Two notebooks are interleaved page by page and become nearly impossible to pull apart.
Newton's Cradle	★★☆	★☆☆	★☆☆	A Newton’s cradle demonstrates conservation of momentum and energy through swinging metal spheres that collide in sequence. When one or more spheres are released, the same number of spheres on the opposite side swing out with nearly identical motion.
Rolling a Soda Can With Static Electricity	★☆☆	★☆☆	★☆☆	A balloon rubbed on hair or fabric becomes charged with static electricity. When brought near an aluminium can lying on its side, the can rolls toward the balloon without being touched, demonstrating electrostatic attraction and the movement of charges in conductors.
Rotating Chair with Dumbbells	★★☆	★☆☆	★★☆	A person seated on a rotating chair holds dumbbells with arms extended. As the person pulls the dumbbells inward, the chair spins faster, demonstrating conservation of angular momentum. Extending the arms again slows the rotation.
Simple Accelerometer	★☆☆	★☆☆	★☆☆	This demonstration uses a cork suspended in water inside a jar to show how acceleration affects fluids and objects. Instead of moving opposite to acceleration as many students expect, the cork moves in the same direction as acceleration because of pressure differences in the water.
Surface Friction	★★☆	★☆☆	★☆☆	Students drag a wooden block over different surfaces using a spring scale, recording the steady pulling force to compare kinetic friction. Results are analyzed across at least three trials per surface and used to discuss variables, error sources, and friction concepts.
Toppling Bottles	★☆☆	★☆☆	★☆☆	Three bottles - one empty, one full of water, and one half-full - are placed on a tilted board to compare their stability. Students observe that the bottle with the lowest center of gravity (the half-full one) is more stable than the empty or full bottles.
Tug-of-War Vector Addition	★☆☆	★☆☆	★★☆	A tug-of-war setup demonstrates how forces act as vectors. People or teams pulling on a central ring or rope represent individual force vectors. If the pulls are balanced, the ring stays still; if unbalanced, the ring moves in the direction of the resultant force.

Materials
★☆☆ Easy to get from supermarket or hardware store
★★☆ Available in most school laboratories or specialist stores
★★★ Requires materials not commonly found in school laboratories

Difficulty
★☆☆ Can be easily done by most teenagers
★★☆ Available in most school laboratories or specialist stores
★★★ Requires a more experienced teacher

Safety
★☆☆ Minimal safety procedures required
★★☆ Some safety precautions required to perform safely
★★★ Only to be attempted with adequate safety procedures and trained staff