Force
Force is everywhere in our daily life. When you walk, your feet push against the ground, and the ground helps push you forward. When you throw a ball, the force from your hand makes it move. When the ball falls, gravity pulls it toward Earth.
The amount of force is measured in newtons (N) using a device called a force meter or newton meter. A stronger push or pull means a greater force.
An important idea is that a force can change an object's motion. A heavier object usually needs more force than a lighter object to produce the same change in motion. Friction can also oppose movement, which is why a rolling ball eventually slows down and stops.
Forces often act together. Scientists use arrows to show forces: the arrow points in the direction of the force, and a longer arrow represents a stronger force.