# Dynamics

Apply and sense force, torque, and motion

Model and sense forces, torques, and motion variables. You can model joint actuation inputs and internal mechanics, external loads, interactions between bodies, and gravity. You can sense position, velocity, and acceleration as well as various types of forces and torques.

For an overview of the dynamical variables that you can model and sense, see Modeling and Sensing System Dynamics. For an example showing how to actuate a joint, see Specify Joint Actuation Torque. For an example showing how to sense trajectory coordinates, see Sense Motion.

## Simscape Blocks

 External Force and Torque General force and torque arising outside the modeled system Gravitational Field Field of force due to point mass Internal Force General force acting reciprocally between two frame origins Inverse Square Law Force Force proportional to the inverse square distance between two frame origins Spring and Damper Force Force proportional to the distance and relative velocity between two frame origins
 Transform Sensor Sensor that measures the spatial relationship between two frames
 Mechanism Configuration Mechanism-wide simulation and mechanical parameters

## Examples and How To

### Sense Force, Torque, and Motion Outputs

Sense Motion

Use the Transform Sensor block to sense frame motion in a simple multibody model.

Sense Constraint Forces

Use the sensing capability of a joint block to sense the internal forces acting on a mechanical link.

Sense Forces and Torques Acting at Joints

Use the sensing capability of joint blocks to measure the forces and torques acting at a joint.

Analyze Motion at Various Parameter Values

Simulate a four-bar model at different coupler link lengths and plot the resulting coupler curves.

### Prescribe Force, Torque, and Motion Inputs

Specify Joint Actuation Torque

Use the actuation capability of a joint block to specify the actuation torque on a joint.

Prescribe Joint Motion in Planar Manipulator Model

Use the actuation capability of joint blocks to specify the trajectory of frame.

Specify Joint Motion Profile

Use the actuation capability of joint blocks to specify the trajectory of a frame.

Model Gravity in a Planetary System

Assemble a system of gravitationally-bound free bodies using Cartesian Joint and Gravitational Field blocks.

## Concepts

### Force and Torque Specification

Modeling and Sensing System Dynamics

Workflow steps for setting and sensing dynamic quantities such as force, torque, position, and more.

Modeling Gravity

Modeling the effects of uniform gravity, gravitational fields, and individual gravitational forces. Software definition of rigid body boundaries and its impact on gravitational torques.

Joint Actuation

Joint actuation modes, motion input handling, and key differences between model assembly and simulation.

Actuating and Sensing with Physical Signals

Using physical signals to specify actuation inputs and obtain sensing outputs.

### Motion, Force, and Torque Sensing

Force and Torque Sensing

Forces and torques that you can sense and the blocks that you can use to sense them.

Motion Sensing

Motion variables that you can sense and the blocks that you can use to sense them.

Translational Measurements

Translational variables that you can sense and the blocks that you can use to sense them.

Rotational Measurements

Rotational motion variables that you can sense and the blocks that you can use to sense them.

Measurement Frames

Measurement frame definition and summary of measurement frame types.

## Troubleshooting

Joint Actuation Limitations

Restrictions and special considerations for models with motion actuation inputs in joint blocks.

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