Motion Summary Notes
Recall (from previous years)

Energy can be present in different forms. Moving objects have kinetic energy. Stored energy that can be released as other forms of energy is called potential energy. 
Energy can never be destroyed but can be converted into different forms. 
A force is exerted when an energy change causes an object to move or change shape. (Unless another force balances it). 
Friction is a contact force which opposes motion and affects many everyday situations. 
Gravity is the force of attraction that every object exerts on every other object but it is only noticeable when one of the objects is very large. 
A field is the area in space where a force can act. e.g. there is a gravitational field around the Earth.
Describe the rel
ationship between the change in an object’s position in a certain time as its speed
(or velocity). (1)

Speed: how fast an object is moving, or the distance travelled in the time taken

Velocity: Speed in a given direction

Average speed: The speed at which an object would have travelled if it went the same speed all the time

Instantaneous speed: Speed at any given point at any given moment
Describe the relationship between the change in an object’s speed in a certain time as its
acceleration. (2)
Acceleration:
is The rate at which an object’s speed/velocity changes, when you accelerate your speed
is changing, the closer the dots on ticker timer tape are the slower, the further apart the faster the object is travelling.
Conversions

To convert m/s to km/h,
multiply
by 3.6

To convert km/h to m/s,
divide
by 3.6
FORMULAS:

Average Speed:
Distance travelled Time Taken

Velocity:
Distance Time with direction

Distance:
Velocity x Time

Time:
Distance Velocity

V
av
:
Velocity + Initial Velocity 2
Acceleration (m/s
2
):
change in speed (m) time taken for change (s) EXAMPLE OF ACCELERATION:
A tram increases speed from 6m/s to 10m/s in 2 seconds. Find its acceleration.
(Where u is the initial speed and v is the final speed). A =
=
=
= 2m/s
2
EXAMPLE OF DECLERATION:
A car travelling at 20m/s slows down to 10m/s in 4 seconds. Find the deceleration.
A =
=
=
= 2.5m/s
2
Define that a (unbalanced) force causes acceleration (change in speed) but the amount of change depends on the mass of the object. (3) Use the correct symbols for quantities and their units (4)
Quantity Symbol Unit Symbol
distance d metres m kilometres km time t seconds s hours h speed v or u metres per second m/s kilometres per hour km/h acceleration a metres per second per second m/s/s mass m kilograms kg force F Newtons N
Note that a force will either cause a change in the rate an object’s motion (speed) or in the
direction of its motion. Both are accelerations. (5)
Outline Newton’s 3 laws:
(6)
1.
An object will continue to move with constant speed in a straight line unless acted on by a net force. a.
Also known as the law of inertia 2.
Force is the product of mass times acceleration a.
F = Ma (force = mass x acceleration) i.
F (force) = Newtons (N) ii.
M (mass) = kilograms (kg) iii.
A (acceleration) = metres per second squared m/s
2
b.
When an external force is applied to an object it causes it to accelerate c.
The greater the force that is applied, the greater the acceleration. The lesser the force that is applied, the slower the acceleration.
3.
For every force that acts there also acts an equal and opposite force. a.
Law of action and reaction b.
States that forces must ALWAYS occur in pairs
Apply Newton’s laws of motion.
(7)
1.
An object will to continue to move with constant speed in a straight line unless acted on by an external force 2.
Force is equal to mass times acceleration 3.
For every external force, there is also a reaction force that is equal in size and acts in the opposite direction
Use the term “inertia” in association with Newton’s first law.
(8)
Inertia
–
an objects tendency to resist a change in its motion The larger the mass of an object the greater in inertia. Why station wagons carrying heavy loads should have a strong grill between the back and passenger compartment? When heavy loads are being carried, when the breaks are applied suddenly the objects will continue to travel at the same speed and moves forward due to inertia. A grill will prevent any injuries to the people at the front of the car.
Describe braking as the conversion of kinetic energy to heat by friction. (9)
Analyse common situations, including car crashes, in terms of Newton’s laws.
(10)
An example: ‘you
are travelling in a car at 60 km per hour sitting in the front not wearing a seat belt’ –
your body is moving at 0km/h relative to the car, then the car crashes in the tree, the force acted on the car makes it stop, but you continue onwards toward the windscreen of the car.
Identify and describe safety features that have been developed and incorporated into modern car design. (11)
Effective brakes
–
Helps to decrease stopping distance dramatically by creating greater stopping force for the vehicle to slow/stop in a shorter amount of time
Airbags
–
Airbags cushion the occupant from hitting the dashboard or steering wheel due to the inertial forces that act upon them during an accident or sudden braking. It creates greater stopping force to slow/stop the occupant, thus lessening the occupants stopping distance
Seatbelts
–
Seat belts also provide safety by lessening the inertial forces acting on the occupant, stopping/slowing them from hitting things in from of them by increasing the stopping force
Crumple zones
–
They help dissipate the forces acting upon the car during an accident.