1. Force can change an object's motion

A force can make a stationary object move, speed up a moving object, slow it down, or change its direction. Its effect depends on the object's mass and the net force acting on it.

2. Gravity is a force that attracts objects

Earth's gravity pulls objects toward its center, which is why dropped objects fall toward the ground. Gravity also helps keep the Moon and artificial satellites in orbit.

3. Force is measured in newtons

The SI unit of force is the newton (N), named after physicist Isaac Newton. One newton is the force required to accelerate a mass of 1 kilogram at 1 metre per second squared.

4. Force, mass, and acceleration are connected

Newton's second law states that the net force equals mass multiplied by acceleration. For the same mass, a greater net force produces a greater acceleration.

5. Astronauts in orbit still experience gravity

Astronauts appear weightless because they and their spacecraft are continuously falling around Earth together. Gravity is still acting on them. They are not simply beyond its reach.

6. Some forces act without direct contact

Gravity and electromagnetic forces can act across a distance. For example, a magnet can attract certain metal objects without touching them.

7. Friction helps us walk

Friction between your shoes and the ground provides the grip needed to walk without slipping. Without sufficient friction, starting, stopping, and turning would be much more difficult.

8. Rockets move by pushing gas backward

A rocket expels gas in one direction, producing thrust in the opposite direction. This works even in the vacuum of space because a rocket does not need air to push against.

9. Forces always come in interaction pairs

Newton's third law states that when one object exerts a force on another, the second exerts an equal and opposite force on the first. These forces act on different objects, so they don't cancel each other on a single object.

10. Seat belts use the physics of motion

When a car stops suddenly, passengers tend to keep moving forward due to inertia. Seat belts exert a force that helps slow passengers down safely with the vehicle.

11. Balanced forces can keep an object at rest

When the forces acting on an object cancel out, the net force is zero. The object can remain at rest or continue moving at a constant velocity.

12. Force can cause rotation

A force applied at a distance from a pivot can produce torque, which tends to rotate an object. This is why a longer wrench can make loosening a tight bolt easier.

13. Force can change an object's shape

Stretching a rubber band, compressing a spring, or squeezing a sponge applies force that deforms the object. Some materials return to their original shape when the force is removed.

14. The Moon's gravity helps create ocean tides

The Moon's gravitational attraction contributes to the ocean's tidal bulges. The Sun's gravity also affects tides, and the alignment of the Sun, Moon, and Earth influences tidal ranges.

15. Nature has four fundamental interactions

Physics describes four fundamental interactions: gravitational, electromagnetic, strong nuclear, and weak nuclear. The strong interaction helps bind atomic nuclei together, while the weak interaction plays a role in certain forms of radioactive decay.