# linear(duration:) An animation that moves at a constant speed during a specified duration. ``` static func linear(duration: TimeInterval) -> Animation ``` ## Parameters `duration` The length of time, expressed in seconds, that the animation takes to complete. ## Return Value A linear animation with a specified duration. ## Discussion A linear animation provides a mechanical feel to the motion because its speed is consistent from start to finish of the animation. This constant speed makes a linear animation ideal for animating the movement of objects where changes in the speed might feel awkward, such as with an activity indicator. Use `linear(duration:)` when you want to specify the time it takes for the animation to complete. Otherwise, use [`linear`](/documentation/SwiftUI/Animation/linear) to perform the animation for a default length of time. The following code shows an example of using linear animation with a duration of two seconds to animate the movement of a circle as it moves between the leading and trailing edges of the view. The color of the circle also animates from red to blue as it moves across the view. ``` struct ContentView: View { @State private var isActive = false var body: some View { VStack(alignment: isActive ? .trailing : .leading) { Circle() .fill(isActive ? Color.red : Color.blue) .frame(width: 50, height: 50) Button("Animate") { withAnimation(.linear(duration: 2.0)) { isActive.toggle() } } .frame(maxWidth: .infinity) } } } ```  --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)