OCR Physics Year 1 - Topic 3.5 Newton's Laws of Motion and Momentum

Vocabulary flashcards covering Newton's three laws of motion, linear momentum, impulse, force-time graphs, and elastic versus inelastic collisions.

Newton's first law

A body will remain at rest or continue to move in a straight line at a constant velocity unless an external force acts on it.

Newton's second law

The resultant force on an object is proportional to the rate of change of momentum of the object, and the momentum change takes place in the direction of the force.

Newton's third law

If object A exerts a force on object B, then object B will exert an equal and opposite force on object A.

Newton's second law equation (constant mass)

$F = ma$, where $F$ is the resultant force, $m$ is the mass of the body, and $a$ is the resulting acceleration.

Requirements for Newton's third law force pairs

The forces involved must be of the same type and must be acting in opposite directions on different objects.

Linear momentum

The product of an object's mass and velocity ($p = mv$), measured in units of $kg\,m\,s^{-1}$.

Principle of conservation of momentum

The total momentum before a collision is always equal to the total momentum after the collision, provided that no external forces are involved.

Impulse

The product of a force $F$ and the time $\Delta t$ for which the force acts ($\text{Impulse} = F \Delta t$), measured in $N\,s$ or $kg\,m\,s^{-1}$.

Net force in terms of momentum

The rate of change of momentum, expressed as $F = \frac{\Delta p}{\Delta t}$.

Area beneath a force-time graph

The property equal to the impulse of the force, which is also equal to the total change in momentum of the object.

Elastic collision

A collision in which both total momentum and kinetic energy are conserved, meaning no energy is transferred to other forms such as heat or sound.

Inelastic collision

A collision in which momentum is conserved, but some of the kinetic energy is transferred to other forms of energy in the collision.

Collisions in two dimensions

Collisions not taking place in a straight line, where momentum must be conserved independently in two perpendicular directions (e.g., along the $x$-axis and $y$-axis).