P2 (1)
Speed
Average Speed
Velocity and Acceleration
speed(m/s) = total distance travelled(m) / time taken(s)
On a Graph
Distance Time Graph(shows the distance and object moves in a period of time)
The gradient at any point shows the speed at that time
Gradient- M = Y/X
Acceleration(m/s2) = change in velocity(m/s) / time taken(s)
Velocity(an object's speed in a given direction)
Change of velocity = final velocity- original velocity
Using Velocity time graphs
Show how an object's velocity changes with time. Gradient = Accleration
Flat Line = Constant Speed
Area under a velocity time graph = distance travelled
Forcing it
How things Move
Using Resultant Forces
In a vehicle, fuel consumption increases if drag forces increases at a certain speed
More energy is needed to overcome the larger drag and travel at the same speed
Forces and Acceleration
investigating aceleration
If there is a resultant forces, the object accelerates in the direction of the unbalanced force
Acceleration (m/s2) = force(N) / mass(kg)
Mass Increase = Acceleration decrese
Force applied increases = Acceleration increase
Mass in Space
Weight depends on mass and gravity
To find mass in space, a known force as to be applied and the acceleration need sot be measured
Balanced Forces
Forces on Moving Objects
For every force, there is an equal sized force acting in the opposite direction
EG
When sitting on a chair, it pushes as hard as you push down on it
When a parachute is pulled, the weight of the diver is matched by the upwards tension in the parachute strings
Lift
When a lift accelerates upwards, the force from the floor pushing upwards is greater than the weight of the person is lifted. The person feels heavier than normal
Stop
Thinking and Braking
Total Stopping Distance = thinking time + braking distance
Reaction time = time taken for a driver to react to a harzrd
Thinking Distance = Speed x Reaction time(increases if the driver is tired, distracted or has taken alcohol or drugs)
Braking distance = distance travelled while the brakes are applied(increases if the road is wet or icy, the tyres are worn down, brakes are in bad conditions)
Aquaplaning
Water from the surface of a wet road is channelled out through the treads on a tyre.
If the tyre thread is worn, water cannot be removed so the car slides over a layer of water on the road and cannot be controlled
Terminal Velocity
Drag forces increases as an object moves faster(every moving object experiences and force in the opposite directions)
Resultant Force = the difference between the force causing motion and drag forces
weight(N) = mass(kg) x gravity(N/kg)
Skydiver
Feels a constant speed
As they accelerate, drag forces match his weight and he reaches a top speed(terminal velocity)
When the parachute is opened, drag forces increase, the resultant upwards forces decelerates and drag force decrease until he reaches a slower terminal velocity
Forces and Elasticity
Elastic Object
the extension is proportional to the force applied up to a limit
above the limit, extension is not proportional to the force
Hooke's law
Using Elastic Potential Energy
Whenever an elastic object is stretched or squashed, work is done to change its shape(stored as elastic potential energy)
Energy can be transferred(EG bow or catapult)
Energy to Move
Kinetic Energy transfers
Transferred by- From chemical energy in food a person eats, From chemical energy in fuel used in an engine
Kinetic Energy is transferred to the surroundings as a result of frictional forces- Friction between car tyres and the road surfaces, Air resistance felt by aircraft and other moving objects
Kinetic Energy transfer can be useful- Regenerative breaks slow down the car using the engine(used to charge the battery's), In a car crash, car crumble zones are designed to distort, absorbing kinetic energy
Storing Kinetic Energy
Flywheels are heavy, fast-spinning wheels that store kinetic energy for short periods of time
Working Hard
How Much and How Far?
Work Done(J) = Force(N) x Distance moved in the direction of the force(m)
Work is done, and energy is transferred whenever a force moves
A smaller force is needed to drag something up a ramp compared with lifting it directly. The force along the ramp is working over a longer distance, and also needs to work against friction
The clock's stopped!
When the battery runs out, clocks stop with their moving hands in the 'quarter to' position. Most work must be done to lift the hand upwards per tick in this position
Energy in Quantity
Calculating Gravitational Potential Energy
Gravitational Energy = energy an object has because of its position
The higher the object is lifted above the ground, the more energy the object gains
Gravitational Potential Energy(joules) = mass(kg) x gravity(N/kg) x height(m)
Investigating Kinetic Energy
Kinetic Energy(J) = 1/2 x mass(kg) x velocity2 (m/s)2
At its highest point, a pendulum has gravitational potential energy and no kinetic energy. As it swings, some gravitational energy changes to kinetic energy and back again