Answer:
valves
The heart has four valves - one for each chamber of the heart. The valves keep blood moving through the heart in the right direction.
The Wheel & Axle. The wheel has always been considered a major invention in the history of mankind
The Inclined Plane
The Wedge
The Pulley
The Screw
Answer:
An object changes position if it moves relative to a reference point. The change in position is determined by the distance and direction of an object's change in position from the starting point (displacement). Direction • Direction is the line, or path along which something is moving, pointing, or aiming.
Explanation:
1. Frequency 2. measure from trough to trough