Why Is Clock Pendulum Made of Invar?

Invar is a nickel-iron alloy which is known for its low coefficient of thermal expansion. Since, its length remains almost constant for temperature change, therefore it is used to make the clock's pendulum.

Why do we use invar in clocks?

Invar is an alloy which has a small coefficient of linear expansion. The length of a pendulum made of invar does not change with temperature and hence the time period of oscillation remains the same. Hence the time shown by the clock is accurate. That's why 'invar' is used for making the pendulum of a clock.

What material is the pendulum of clock and why?

Steel is used for the pendulum rod in simple ordinary clocks because it is cheap and has relatively low thermal expansion. Wood is sometimes recommended because of its low linear thermal expansion coefficient along the grain, but it is an inherently unstable material.