Physics : CP1 Forces and Motion : GCSE Cards

Scalar = scalar quantities only have a magnitude or size

• Temperature
• Mass
• Energy
• Distance
• Speed
• Time
• Density

Vector = vector quantities have both a magnitude and direction

• Force
• Weight
• Displacement
• Velocity
• Acceleration
• Momentum

Distance = How far an object had travelled

Speed = how fast or slow an object is traveling

Distance = Speed x Time

Speed = Distance / Time

Time = Distance / Speed

Typical speeds:

• Walking = 1.5 m/s
• Running =  m/s
• Cycling = 6 m/s
• Car       = 13 - 30 m/s
• Train     = 50 m/s
• Aeroplane = 250 m/s

Measuring speeds in th lab

To calculate the speed of an object two measurements are needed:

• How far it travels
• The time it takes to move that distance

The equpment used:

• Ruler and stopwatch = ruler measures distance travelled = stopwatch measures time taken
• Light gates = size of object, measured with a ruler = light gate connects to a timer, which gives                       the reading
• Video analysis = Distance moved from frame to frame observed on a ruler in the pictures = The                            time between frames is known

Distance / time graphs

• A horizontal line on a distance time graph shows that the object is stationairy
• A sloping line on a distance time graph shows that the object is moving
• The speed of an object can be calculaed from the gradient of a distance time graph 

Acceleration

Acceleration = The change in velocity in a given time

a = v-u / t

• If an object is slowing down, it is decelerating (and its acceleration has a negative value)

Velocity-time graphs

• A horisontal line on a velocity-time graph, shows that the object is at contant velocity
• A sloping line on a velocity-time graph, shows that the object is accelerating
• The gradient of the line is equal to the acceleration of the object

Calculating the distance travelled

• Find the area under the graph will give you the displacement

Uniform acceleration

• Unifrom acceleration = Constant acceleration

v2 - u2 = 2 x a x X

Newton's first law

An object remains in the same state of motion unless a resultant force acts on it. If the resulttant force on an object is zero, this means:

• a stationairy object stays stationairy
• a movng object continues to move at the same velocity (at the same speed and in the same direction)

Relsultant force = A single force that replaces a system of forces

Uniform motion = Constant velocity

• (E.G), When a car travels at a constant velocity, the driving force from the engine is balanced by the resistance force such as air resistance and the frictional forces in the cars moving parts. atahe resultant force on the car is zero.

Air resistance = A force of friction produced when an object moves hrough the air

Terminal velocity = The maximum speed of an object, reached when the forces moving the object                                  are balanced by it's frictional force

Examples of non unifrom motion

Newton's first law can also be used to explain the movement of object traveling with non uifrom motion. This includes situations when the speed changes, the direction changes, or both change.

Newton' seccond law

Resultant force = Mass x Acceleration

F = m x a

• The accelerationof an object increases if the resultant force on it increaces, and decreaces if the mass od the object increaces
• The ratio of force over acceleration is called inertial mass.

Inertial mass = A measure of how difficult is to change thr velocity of an object. It is defined as the                           ratio of force over acceleration

Newton's third law

• Whenever two objects interact, they exert equal and opposite forces on each other 

Examples of force pairs

• Car tyre on the road - There are conact forces between the tyre and the road: The tyre pushes the rod backwards, the road pushes the tyre forwards. These forces are equal in size and opposite in direction.

Weight Mass and Gravitational field strenghth

• The weight od an object may ne though af as acting at a single point called it's centre of mass.
• Depending on the object's shape, it's centre of mass can be inside or outside it.

Cenre of mass = The point representing the mean position of the matter in a body

The weight of an object and it's mass are directly proportional. For a given gravitational field strength, the greater the mass - the greater it's weight is.

weight = Mass x Gravitational field strength

W = m x g

Stoping distances

Stoping distance = Thinking distance + Braking distance

Thinking distance - Is the distance a vehicle travels in the time it takes for the driver to apply the braes after realising they need o stop

Braking distance - Is the distance a vehicle travels in the time after the river has applied the brake

Typical reaction time - 0.2s, 

• A drivers reaction time can be affected by tiredness, drugs, alcohol and distraction
• Longer reaction times increace the thinking distance when stopping froma given speed

Braking distance

• The braking distance of a vehicle can be increased by: Poor road and weather conditions, Poor vehicle conditions, More mass in the vehicle
• When a force is applied to the brakes of a vehicle, there is work done by the friction