# Dynamics

Apply and sense force, torque, and motion

Add forces, torques, and motion inputs to drive your model and use sensors to measure its dynamic response. Use the joint blocks in your model to actuate those joints, model their internal mechanics, and sense joint-specific dynamic variables. Only Joints blocks allow you to specify trajectories in a model.

Use Forces and Torques blocks to model interactions between unconnected bodies or to add special dynamic elements such as gravitational fields and nonlinear spring-dampers—the latter using the generic Internal Force block. You can sense the relative motions of unconnected bodies using the Transform Sensor block.

## Simscape Blocks

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 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 Spatial Contact Force Apply contact forces between a pair of connected bodies Spring and Damper Force Force proportional to the distance and relative velocity between two frame origins
 Transform Sensor Sensor that measures the relative spatial relationship between two frames
 Mechanism Configuration Mechanism-wide simulation and mechanical parameters

## Topics

### Sense Force, Torque, and Motion Outputs

Analyze Motion at Various Parameter Values

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

Sensing

Dynamic variables that you can sense and blocks that you can use to sense them.

Sense Motion Using a Transform Sensor Block

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.

### Prescribe Force, Torque, and Motion Inputs

Modeling Contact Force Between Two Solids

Use the Spatial Contact Force block to model normal and frictional forces between solid blocks.

Model Wheel Contact in a Car

Use the Spatial Contact Force block to model the wheels of a car rolling down a ramp.

Model Gravity in a Planetary System

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

Prescribe Joint Motion in Planar Manipulator Model

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

Specify Joint Actuation Torque

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

Specify Joint Motion Profile

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

Use Contact Proxies to Simulate Contact

Use contact proxies to increase the speed and robustness of contact simulations.

### Force and Torque Specification

Actuating and Sensing with Physical Signals

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

Joint Actuation Limitations

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

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 body boundaries and its impact on gravitational torques.

Specifying Joint Actuation Inputs

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

### 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.

Selecting a Measurement Frame

Measurement frame definition and summary of measurement frame types.

Motion Sensing

Motion 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.

Translational Measurements

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