Forces and Motion

What does a distance–time graph show?

It shows how distance changes over time. The gradient represents speed — a steeper line means faster motion, a flat line means the object is stationary.

How can you find acceleration using a velocity–time graph?

The gradient of a v–t graph gives acceleration. A positive slope =acceleration, a negative slope = deceleration.

How can you measure speed experimentally?

Measure the time to travel a known distance using a stopwatch or light gates, then use v=d/t

How do you find distance from a velocity–time graph?

The area under the graph equals total distance.

What is v2=u2+2as used for?

It links velocity, acceleration, and displacement when time isn’t known.

What is the difference between vector and scalar quantities?

Scalars have magnitude only (e.g. speed, mass). Vectors have magnitude and direction (e.g. velocity, force).

How do you draw force diagrams?

Represent the object as a box or point; draw arrows for all forces. Arrow size = magnitude, direction = direction of force. Example: Falling object → weight down, air resistance up.

What are basic facts about friction and air resistance?

They are resistive forces opposing motion. Friction increases with roughness and weight; air resistance increases with speed and surface area.

What is 𝑊=𝑚𝑔

Weight = mass × gravitational field strength.

What factors increase thinking distance?

tiredness, alcohol, drugs, distractions, or higher speed.

What factors increase braking distance?

Greater speed, heavier vehicle, worn tyres/brakes, wet or icy roads.

What forces act on a falling body?

Weight (downwards) and air resistance (upwards). Weight is constant; air resistance increases with speed.

How does a body reach terminal velocity?

It accelerates until air resistance = weight → no resultant force → constant speed.

What does Hooke’s Law state?

Extension is proportional to force until the elastic limit: 𝐹=𝑘𝑥

What does a force–extension graph show?

Straight line = elastic region. After the elastic limit, the line curves and deformation becomes permanent.

What is elastic vs inelastic behaviour?

Elastic: returns to original shape after force removed. Inelastic: permanently deformed after stretching beyond the elastic limit.

What is the formula for momentum?

P=mv Momentum= massx speed

What is conservation of momentum?

Total momentum before = total momentum after in a closed system.

How do safety features use momentum and time?

Increasing the time of impact reduces force: F=Δp/t  Airbags and crumple zones increase collision time → less force.

What are Newton’s three laws of motion?

1. Object stays at rest/moves at constant speed unless a resultant force acts.

2. F=ma

3. Every action has an equal and opposite reaction.

How do you calculate turning moments?

Moment=Force×perpendicular distance from pivot

How do you find the centre of gravity?

Hang the object from a point, draw a vertical line down. Repeat from another point — the intersection is the centre of gravity.

How do you use balanced moments to calculate forces?

At equilibrium: total clockwise moments = total anticlockwise

How do forces depend on distance from the pivot?

A longer distance produces a larger moment for the same force.