Mass (PB)

R2026b

Point mass with gravitational effects

Since R2024b

• 

Mass (PB) block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
Simscape / Foundation Library / Translational / Elements

Description

The Mass (PB) block represents a point mass with gravitational effects that moves along an inclined rail. Gravity can induce motion along the rail. The force flow equations are:

$$f_{acc}=m\cdot \dot{v}$$

$$f_{acc}=f+f_{gp}$$

$$f_{gp}=-m\cdot g\cdot \sin (\beta )$$

where:

• f_acc is force proportional to mass acceleration. Positive force accelerates the mass in the positive direction.

• f is port force, force of the other mechanical components in the network acting on the mass.

• f_gp is force proportional to the parallel component of gravitational acceleration, that is, to the gravitational acceleration acting along the rail.

• m is the mass.

• v is the mass velocity.

• g is the gravitational acceleration.

• β is the rail incline angle.

The Mechanical Translational Properties (PB) block specifies the gravitational acceleration and rail incline angle in the network. For more information, see Interpreting Logged Forces in Mass Blocks.

Variables

To set the priority and initial target values for the block variables prior to simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. Nominal values can come from different sources, one of which is the Nominal Values section in the block dialog box or Property Inspector. For more information, see Modify Nominal Values for a Block Variable.

Examples

Force Flow in the Position-Based Translational Domain

Describes how to interpret forces in a Simscape™ mechanical position-based translational network. The example summarizes rules for interpreting the signs of logged forces and then considers forces in three types of systems: springs being pulled or pushed from different ends, simple systems with external forces applied at a mid-point, and a more complex system with an external force applied at the mid-point.

• Open Live Script

Gravity and Friction in the Position-Based Translational Domain

Configure gravity and friction due to gravity in a mechanical position-based translational network.

• Open Live Script

Ports

Conserving

R — Port that connects mass to the circuit

position-based translational

Position-based translational conserving port that connects the mass to the physical network.

Programmatic Use

Port: R

Parameters

Mass — Constant mass

1 kg (default) | positive scalar

Mass value. The mass is constant during simulation.

Programmatic Use

Parameter: mass

Programmatic Use: Add Block

To add the block programmatically, use the add_block function with one of these library block paths as the source.

"fl_lib/Translational/Elements/Mass (PB)"

Example: add_block("fl_lib/Translational/Elements/Mass (PB)","myModel/myBlock",MakeNameUnique="on")

For information about programmatic access to individual block parameters, see the Programmatic Use section of parameter descriptions on this page.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2024b

R2026a: Change to block variables

The Accelerational force variable, which is the force proportional to mass acceleration, has been renamed to Mass force and removed from the Initial Targets section of the block dialog box. Instead, you can now specify initial target for the Net force variable, which is the net force of the other mechanical components in the network acting on the mass.

In most models, this change has no compatibility impact. However, if your network is not horizontal and the Accelerational force variable had high or low initialization priority, you must calculate the new initial value for Net force by using the equations in the block description, otherwise your simulation results might change.