In I/GCSE Physics, a **force** is a **push or pull** of one body on another.

Force is a **vector quantity**. It changes in **size and direction**. Other examples of vector quantities include velocity, acceleration and momentum. Scalar quantities** only change in size**, for example, temperature. Forces are measured in **newtons (N)**.__ 1kg is equivalent to about 10N__.

Looking back at the right picture, if the forces are all equal and then cancel each other out, the forces and **balanced **and therefore, the **unbalanced force is zero**. If you look at the left picture, you can see that the forces are not equal. The skater is moving right at 120N, cancelling out the 100N. Here, there is an unbalanced force or **resultant force** of 120-100 = 20N in the I/GCSE physics curriculum.

Newton’s Laws of Motion

- Newton’s
**1st Law**: If the forces on an object is balanced – there is**no resultant force**– the object will either remain**at rest**or**carry on moving at constant speed**in a straight line. If the forces on an object is unbalanced, the object will**accelerate**. - Newton’s
**2nd Law**: Resultant force (N) = mass (kg) x acceleration (m/s2) or**F = ma** - Newton’s
**3rd Law**: For every action there is an**equal and opposite reaction**as highlighted in the I/GCSE physics

That's all for this topic!