Science: Physics
Formula Sheet:
Second Law: F=MxA
Weight can be calculated through the formula:
Fg= mg
Displacement = final position - initial position
Δd = dfinal – dinitial
Speed = distance/time or s=d/t
Velocity = displacement/time or v=Δd/t
Average speed = total distance travelled/total time taken
Average velocity= total displacement/total time
Average Acceleration
= change in speed/time or final speed - initial speed/ time
Forces and Motion:
A force is a push, pull or twist.
Different types of Forces:
Magnetism
The force that enables compasses to work
Air resistance
The force you get when an object moves through the air
Gravity
The force that exists between all objects with mass
Attractive force that exists between all masses.
Larger the mass is, the greater the gravitational attraction.
Your weight is the pull of the Earth’s gravity on your body
Electrostatic
The force you get between two charged objects
Nuclear
The force that holds the nucleus together
Tension
The force you get when a material is being stretched
Compression
The force you get when a material is being squashed
Friction
The force you get when two materials are rubbed together
Always acts in the opposite direction to the way it's moving
**Object will only start to move if it overcomes any frictional forces
Attractive and repulsive forces:
An attractive force is when objects exert a pull on each other, making them want to move closer together. A repulsive force is when objects push each other away.
A force can either be attractive or repulsive or both.
Eg:
Magnetism - Attractive and repulsive
Gravity - Attractive always
Electrostatic - Attractive and repulsive
Contact Forces:
If two objects or materials need to be touching for the force to have an effect then it is a contact force.
Eg: Friction, Air Resistance
Non-contact forces:
If two objects or materials do not need to be touching for the force to have an effect then it is a non-contact force.
Eg: Gravity, Electrostatic, Magnetic
Resistive/reaction forces - A force that acts in the opposite direction to the action force.
Thrust - A forward push.
Upthrust - The upwards force in a body in a liquid or a gas. Force that pushes things upwards
Driving Forces - The forces involved in an event's acceleration into a specific direction
An action force is a force that is applied to an object. A reaction force is a consequence of an action force which is opposite in direction.
Balanced forces
Forces of equal magnitude but are opposite in direction. Objects acted upon by balanced forces remain at rest or stay in motion at a constant speed.
Balanced forces result in constant velocity / speed or remaining stationary
Unbalanced forces
Not equal in magnitude and may or may not be directed in the same direction.
Unbalanced forces result in acceleration or deceleration (negative acceleration)
Mass and Weight:
Mass is a measure of how many particles there are in your body.
Weight is the measure of the pull of gravity on your body.
Weight can be calculated through the formula:
Fg= mg
m= mass in kilograms
g= Earth’s gravitational field in N/kg = 9.8N/kg
Ch 8.5 1,2,4,5,6,8,10a-c
Physics (Newton):
First Law: Law of inertia
An object remains in rest or in constant motion in a straight line unless acted on by a net unbalanced force
Inertia - the tendency for an object to do nothing or remain at rest
The larger the mass of the object, the more inertia it has and the harder it will be to change its motion.
Second Law: F=MxA
Net Force = mass x acceleration
The acceleration of an object depends on the mass of the object and the amount of force applied.
There is a relationship between force and mass
You need a larger force to accelerate a heavy object from rest than to accelerate a lighter object from rest
Weight is the force of gravity acting on an object. We measure it in Newtons.
Mass is the amount of matter in an object.
Net force = N
Mass = kg
Acceleration = m/s2
Third Law: Equal and opposite
For every action there is an equal and opposite reaction
Action-reaction pairs always act on different objects and therefore cannot cancel each other out
Eg:
Air rushing out of a balloon
Action force: rubber of the balloon contracting
Reaction force: the air rushing out, pushing the balloon forward
Leaning your hand on a wall
Action force: you’re pushing your hand against the wall
Reaction force: the wall is pushing back against your hand
An action force is a force that is applied to an object. A reaction force is a consequence of an action force which is opposite in direction.
Forces, Distance, Displacement, Speed, Velocity & Acceleration:
Scalar - quantities that are fully described by a number. (E.g – mass, time, speed)
Vector - quantities that are fully described by both a number and direction (E.g – displacement, force, acceleration)
Distance (d) - is a measure of the length of the path taken by an object. It is a scalar quantity. Does not depend on direction
Displacement (s) - is a measure of the change in position of an object. It is a vector quantity.
In other words – the shortest path between two points
Does depend on direction
Displacement (Δd) = difference between an object’s final position and its starting position.
Does depend on direction.
Displacement = final position - initial position
Δd = dfinal – dinitial
In order to define displacement, we need directions.
Examples of directions:
+ and –
N, S, E, W
Angles
Speed (s) - Rate at which an object is moving
Speed = distance/time or s=d/t
Does not require a direction - Scalar quantity
Velocity (v) - speed with direction
Velocity = displacement/time or v=Δd/t
Has magnitude and direction
Magnitude (speed) - a measure that has a value
Average Speed and Velocity
Both give indication of how fast an object is moving over a time interval.
Average speed
Average speed = total distance travelled/total time taken
vav=d/t
vav= average speed
Average velocity
v= total displacement/total time
**Has direction
Acceleration
Rate of change of velocity
Vector quantity, eg. magnitude & direction
Written in m s-2 or m/s/s
Positive acceleration indicates object speeding up
Negative acceleration indicates an object slowing down or speeding up in the opposite direction.
Average Acceleration
= change in speed/time or final speed - initial speed/ time
Acceleration due to gravity is 9.8 m/s/s or 1G
Final velocity is called terminal velocity
Position, Velocity Time Graphs:
Describing position-time graphs:
Distance - why?
DIsplacement - why?
Displacement-time graph
Displacement on graph - use axis to calculate
Use units as they are if neg or pos.
Distance on graph - if not available use displacement axis to calculate
Calculate different from starting point to next point and find total between them all.
If line is straight, it means that the object was stationary
Position-time graph
Gradient
The measure of velocity
Can use the rise in the graph to find the change in position, eg. displacement
Velocity-time Graph:
If in positive side velocity is positive, if in negative side velocity is negative
Eg: in a positive direction for the first 6 s. Between the 6 s mark and the 7 s mark she is stationary, then she runs in the reverse direction, i.e. has a negative velocity for the final 3 s.
Displacement in the velocity-time graph can be found by found the area under the graph.
Gradient of the graph gives the acceleration