Physics 2.1&2

Distance - Time graphs:

- Shows distance(m) travelled in how much time(s)  

- Line gradient = speed(m/s)

- Horizonal line if stationary 

Velocity - Time graphs:

- Shows velocity(m/s) of travel in how much time(s)

- Line gradient = acceleration(m/s^2)

- Horizonal line if not accelerating, could still be moving

- Negative gradient = deccelerating

- Area under the graph = distance

Velocity = speed in a specified direction

Velocity changes if the direction changes even if the speed does not change

Acceleration = change in velocity         Negative acceleration value = Decceleration

The acceleration equation is: 

Objects exert equal and opposite force(N) on each other

Forces have: size & direction

- Weight is a force that can only act downwards                  Some forces cancel each other out

Resultant force = the single force that has the same effect as all original forces acting together, the overall force on the object

If resultant force = zero, the object will:

- remain at rest         OR        - continue moving in the same speed and direction

If resultant force = not zero, the object will:

- begin to accelerate in the direction of the force       OR       - continue in resultant force direction

 OR       - decelerate (if it was orginally moving in a different direction to the resultant force)

FOR AN OBJECT TO MOVE THERE MUST BE A RESULTANT FORCE ACTING UPON IT

Resultant force causes acceleration (can be negative)

No acceleration = no resultant force present

A resultant force is needed for an object to change direction 

Resultant force decrease = acceleration decrease    and so...

A larger resultant force = larger acceleration 

The higher the mass, the bigger the force required to reach a given acceleration

Resultant force equation:

F = M x A

(Force = resultant force(N), Mass = (Kg), Acceleration = (m/s^2))

If travelling at a constant speed resultant force = zero as:

driving forces = frictional forces

 - Friction and air resistance oppose the driving force of a moving vehicle

 The faster the speed the more decceleration needed to stop in a particular distance

Braking in a vehicle:

Thinking distance = Time from spotting an obsticle to applying the brakes

Braking distance = Time taken for brakes to stop vehicles once engaged

Stopping distance = Overall time taken for car to stop (thinking + braking distance)

Thinking distance effected by:

- Car speed (more/less distance covered in the time it takes to think)

- Drugs

- Tiredness

- Age (these all effect reaction times)

Braking distance effected by:

- Car speed  (more/less distance covered in the time taken for brakes to slow vehicle)

- Weather (less contact with road so reduced friction)

- Worn tyres / brakes 

- Condition of road (e.g. potholes / bumpy = less friction)

Mass = quantity of matter               Weight = force of gravity acting on the mass

Resultant force of a falling object is gravity, on earth gravity causes an acceleration of 10m/s^2

F = M x A becomes W = M x G 

(F = resultant force in N, M = mass in kg, A = acceleration in m/s^2)

(w = weight in N, M = mass in kg, G = gravity's acceleration in m/s^2)

Terminal Velocity and Equal forces in falling through gas or liquid

Terminal velocity = constant speed of a falling object where resistant stops further acceleration

- When falling, drag or air / fluid resistance slow the body, the faster the fall, the bigger this force

- Eventually the weight (downwards force) will equal the upwards force so the resultant force is zero and the object is no longer acelerating, it has reached terminal velocity.

Elastic = object / material which regains original shape after forces on it are removed

Inelastic = object / material which will not regain its original shape once forces are removed

Extension = increase in length from the spring's original length

- A graph showing spring extension is straight and passes the origin

- The extension is directly proportional to the force applied

- If force is too big line will curve as the limit of proportionality has been exceeded

- Hooke's Law states extension is directly proportional to force applied. The equation for this is:

F = K x E

(F = force in N, K = spring constant in N/m (newtons per meter), E = extension in M)

- Stiffer spring = greater spring constant             - When force removed, stored energy released

- Streching an elastic object means work is done, this is stored as elastic potential energy

Reducing speed reduces fuel consumption, this is fuel economy.

Reducing air resistance (force) by streamlining improves fuel economy.

Speed cameras discourage speeding, deterred by           - Fines         &          - Losing licence

They can be used to determine speed at a particular point.

They can be used in pairs to calcualte an average speed between the two points. 

Skidding = brakes applied fast, wheels lock and slide along surface (increasing stopping distance)

Anti-skid surfaces reduce skidding as they are rougher than normal roads so increase friction.

Used at traffic lights, lights and junctions where braking is likely.