Physics - Motions and Forces, Forces and their effects

impact force

resultant force/impact force = (mass x final velocity) - (mass x initial velocity) / time for collision

gravity

• not a force, field which surrounds an object with mass

• 10 N/kg

• causes gravitational forces + objects to accelerate at 10m

air resistance

• opposes motion of objects that move through the air

• act in the opposite direction to direction of motion

• collision with air particles

• as speed increases so does air resistance

upthrust

produced when object is placed in a fluid and displaces some of that fluid

value of upthrust = weight of displaced fluid

engine force

shows direction an engine on a vehicle is pushing it

momentum

product of an object's mass and velocity.

momentum acts in the same direction as the velocity

resultant force equation

resultant force (N) = mass (kg) x acceleration (m/s2)

momentum equation

momentum (kg m/s) = mass (kg) x velocity (m/s)

acceleration equation

acceleration (m/s2) = final velocity (m/s) - initial velocity (m/s) / time (s)

final velocity equation

final velocity2 (m/s) = initial velocity2 (m/s) + 2as

a = acceleration (m/s2)

s = distance (m)

Newton's 1st Law

an object will remain at rest or continue to move at a constant velocity unless acted upon by a resultant force.

Newton's 2nd Law

the acceleration of an object is directly proportional to the resultant force acting on it. The acceleration and resultant force act in the same direction.

Newton's 3rd Law

if object 'A' exerts a force on object 'B', then object 'B' must exert a force on object 'A' that is equal in magnitude, but acts in the opposite direction.

what are scalars?

physical quantities that only have magnitude

what are vectors?

physical quantities that have magnitude and direction

thinking distance

distance travelled while the driver is reacting

braking distance

distance travelled while braking to a stop

stopping distance equation

stopping distance = thinking distance + braking distance

forces definition

change an objects shape/speed/direction/size

some require contact while others can act over a distance

weight

force of gravity on an object

weight = mass x gravity

friction

opposite direction to that of motion

cause by objects being in contact

static friction = stationary objects

dynamic friction = moving objects

drag

friction and air resistance grouped together

anything acting in opposite direction to that of motion

normal contact force

90° to the contact surface

require contact

thrust

sometimes used instead of engine force on rockets and planes

lift

the upward force wings on planes and rotors on helicopters produce

resultant force

overall or need force acting on an object

vector examples

- gravity

- weight

- lift

- upthrust

- displacement

- velocity

ANY FORCE

scalar examples

- speed

- distance

- time

- temperature

- mass

- density

CENTRIPETAL FORCE

• resultant force producing circular motions

• moves at constant speed but constantly changing velocity as it's direction is changing

• always acts towards centre of circle and is perpendicular to its velocity

Mass

Measure of difficulty to accelerate an object

How much matter it contains

Momentum Units

kg m/s

Physical quantities

Used to measure work around us

acceleration

when the resultant force and the velocity of the object act in the same direction, the object accelerates

deceleration

when the velocity and the resultant force act in opposite direction, the object decelerates

conservation of momentum

- isolated system (no other forces involved)

- momentum is conserved in all collisions

- total momentum before a collision = the total momentum after collision

car safety

- air bags, crumple zones and seat belts reduce impact force in collisions

- these only affect the time of a collision (slowing it down)

Relation ship between weight and up thrust

Floating: weight of fluid is equal to value of upthrust

Sinking: weight> upthrust

Rising: weight

Non-contact forces

gravitational, magnetic, electrostatic

Practical: relationship between force mass and acceleration of trolley moving down a ramp

1. Incline ramp slightly (trolley should move down slope with constant velocity with no weights pulling on it)

2. Acceleration recorded by data logger should be 0m/s^2 (any extra forces acting on the trolley will equal resultant force)

3. Remove masses from top of the trolly and add to the pulling force (keeps mass of trolley constant)

4. Release trolley and record results adding on a slotted mass each time (0-3.5N)

5. Repeat experiment for each resultant forces value to improve reliability

velocity

speed in a stated direction

acceleration in free fall

10m/s^2

how to measure weight

- spring balance

- will strech until force on spring balances weight of object

- spring extension = weight

relationship between weight and GPE

as gravity increases, weight increases

inertial mass

how difficult it is to change velocity of an object

mass = force/acceleration

large decelratations

cause brakes to overheat

driver loses control of vehicle

relationship between speed and distances

speed increases=thinking distance increases

speed and braking distance have a squared relationship (speed doubles, braking quadruples)

factors which affect reaction time

drugs

tiredness

alchohol

distractions