3 Laws of Motion Recap

- First, balanced forces result in no change in velocity.
- Second, the resultant force is equal to the acceleration in that direction.
→ Arrows will be unequal. 
→ Starting, stopping, speeding up, slowing down, or changing direction.
- Third, Reaction forces: Object A applies a force to object B (action), and object B applies an equal and opposing force to object A.
- F = MA → The bigger the force, the greater the acceleration/deceleration.
→ Bigger mass = Smaller acceleration.
→ Smaller → More acceleration = Bigger force

Heavier Objects on Earth

For example, of the basketballs and bowling balls of the same SA + size, only the bowling ball weighs more.
- If we dropped both at the same time, then
low height hit the ground at the same time: 
→ Both experience acceleration due to gravity but wouldn't have been falling long enough to accelerate to a speed where AR was big enough to be a major factor. Neither would've reached their terminal velocity.
- Aeroplane height: Initially, both aircrafts experience the same acceleration due to gravity; as they descend and perform AR, the resultant force and acceleration will both reach their terminal velocity.

Continued

- A heavier bowling ball needs much greater speed before AR is large enough to equal its weight.
- ∴ The terminal velocity of a bowling ball is significantly higher due to its increased weight.
- It can reach the ground faster due to its higher maximum speed.

Terminal Velocity

w = m x g

- Fluid: A liquid or gas 
- Weight: The downward force an object experiences due to gravity.
- Air resistance is a contact force.
- This occurs when objects of the same size are travelling at a constant speed.
- If the weight of the arrows is equal, then resistance is acting on it.
- Air particles are all around us; as an object moves, it collides with our particles. The faster an object moves, the greater the air resistance (AR).
- Vehicles undergo streamlining to minimise AR.
- Falling through a guide will also cause a frictional force (AR) on the object.

Continued

- Freefall: When there's no air resistance (i.e., no air), objects will then fall at the same speed.
- The force of gravity causes all objects to accelerate at the same rate. All objects fall at the same speed unless other forces act.
- Near the surface of the earth, all objects have an acceleration of 9.8 m/s² due to gravity, acceleration due to gravity. 

Free Body Diagrams

- This is the most basic method of depicting the forces acting on an object.
- Only shows forces acting on an isolated object or system (not any other objects/forces, e.g., those that the object exerts on the environment).
- A square or circle represents the object; ensure the arrows are proportionate.

- If the object is on the ground, the normal contact force and weight usually cancel out.

Resultant Forces

- The formula is W = mg (g = 9.81 N/kg on Earth).
- Newton's 3rd law: Every action has an equal and opposite reaction; e.g., if I push on a wall with a force of 10N, then there's a force exerted onto me equal in magnitude but opposite in direction.
→ This is why for all stationary objects, force is not zero everywhere.
- When examining a single object, such as a car, we don't need the forces to be equal in size and opposite in direction.
- Resultant forces are the arrows drawn proportionate to the size of the force.

Continued

- If there are two or more forces acting on an object in a straight line, we can replace them with a single force, known as the resultant force, which has the same effect as all the original forces acting together.

- To find instantaneous speed, draw a tangent on d-t.

Forces and Breaking

- Factors affecting stopping distance = Thinking distance + Braking distance
- Stopping distance = Thinking distance + Braking distance.
- Thinking distance affected by:
- How fast a car is travelling or how intoxicated a person is, the concentration of person and visibility levels.
- Breaking distance affected by:
- The factors to consider include the speed of the vehicle, the condition of the tires, the mass of the vehicle, the effectiveness of the brakes, and the condition of the roads.

Physics Revision

- Acceleration still occurs when on a roundabout, ∴ you're changing direction.
- Velocity + Acceleration + All forces = Vector
- Speed, Mass + Energy = Scalar
- Vector quantities: Magnitude + Direction
- Scalar quantities: Only magnitude
- Distance: How far an object has moved (scalar).
- Displacement (vector): Measures distance and direction in a straight line from object's starting point to finishing.

e.g., walking 5m N + then 5m S 
displacement = 0m, distance = 10m