The Physics of Boulder Drop: Gravity and Surface…

Gravity and Mass

The acceleration due to gravity (g) is approximately 9.81 m/s² near Earth’s surface, acting downward on any object with mass. The force of gravity can be calculated using the equation F = mg, where m is the mass of the boulder and g is the gravitational constant. A heavier boulder will experience a greater gravitational pull, affecting its velocity and impact upon landing.

The mass slider in the simulation allows you to adjust the weight of the boulder, demonstrating how different masses affect the height from which it can be dropped without breaking the simulation’s physics model.

Surface Interaction

The surface on which a falling object lands plays a crucial role in determining its behavior after impact. The restitution and friction coefficients of different surfaces (soil, gravel, granite) influence how the boulder bounces or comes to rest. For example, granite has high hardness and low elasticity compared to soil, leading to fewer bounces but more energy dissipation through heat.

The surface select option in the simulation allows you to observe these differences, illustrating how varying material properties affect the dynamics of a falling object.

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Impact Dynamics

Upon impact with the ground, the boulder experiences both normal force (perpendicular to the surface) and frictional forces (parallel to the surface). The normal force is responsible for the compression of the material at the point of contact, while frictional forces oppose motion. These interactions are governed by Hooke’s Law for elastic deformation and Coulomb’s law for static friction.

The live height, velocity, and kinetic-energy readouts in the simulation provide real-time data on these physical processes, allowing you to observe how energy is conserved or dissipated during each impact.

Energy Conservation

As the boulder falls, its potential energy (PE) converts into kinetic energy (KE). The total mechanical energy remains constant in an ideal scenario without air resistance. However, in real-world scenarios like those simulated here, some of this energy is lost to heat and sound due to deformation and friction at impact.

By manipulating the drop height and observing changes in velocity and kinetic energy, you can explore how these factors influence the overall mechanical energy of the system.

Frequently asked questions

How does mass affect a boulder's fall?

Mass affects the gravitational force acting on the boulder but not its acceleration in free-fall, as both are proportional to g. Heavier boulders will have more kinetic energy at impact and may cause greater deformation upon landing.

What is restitution, and how does it affect the simulation?

Restitution refers to the coefficient of restitution (COR), which measures the ratio of the relative velocity after and before a collision. In the simulation, different surfaces have varying COR values, affecting how much energy is conserved during bounces.

Why do some surfaces cause more dust than others?

Softer or less compacted surfaces like soil tend to create more dust because they are more prone to compression and fragmentation upon impact. Harder surfaces like granite may not produce as much dust but will still show signs of deformation.

How does the simulation model air resistance?

The simulation assumes no significant air resistance, focusing on gravitational and surface interactions. In real-world scenarios, air resistance would affect the boulder's velocity and trajectory, especially at higher speeds or in denser atmospheres.

Try it live

Everything above runs in your browser — open Drop Boulder Simulator (2D) and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Drop Boulder Simulator (2D) simulation

The Physics of Boulder Drop: Gravity and Surface Interaction