Physics section 1: Forces and Motion (COMPLETED) (A (Units (Kilogram …
Physics section 1: Forces and Motion (COMPLETED)
unit of mass
kilogram metre / second
Movement and position
Avg speed = distance moved/ time taken
acceleration = change in velocity / time taken
distance time graph ( area under line = distance travelled)
forces, movement, shape and momentum
When an object is stationary it has an equal force pushing down and up. The downward force being gravity and the upward force being the surface the object is on. The object is not floating but it is not going into the ground.
When an object is accelerating it has the upwards and downwards forces but it also has forwards and backwards forces (drag and friction). The forward force is larger than the backward force when an object is accelerating.
When an object is going at a constant speed it has downward and upward forces as well as forward and backward forces. The forward and backward forces are equal, so the speed doesn't change even though the object is moving.
When an object is decelerating it has the equal upward and downward forces as well as forward and backward forces, but the backward force is larger than the forward one, slowing the object down.
changes in shape affect momentum. Force= change in momentum/ time taken. An example of this is crumple zones in car decrease the force on the passengers.
Which ever direction the force is greatest in will be the direction the object travels in.
An objects centre of gravity is where all of its weight acts through.
drag and friction
acting against motion
Has magnitude and a direction. For example velocity is a speed in a given direction.
Force has magnitude, it is measured in newtons but it acts in a direction.
For example 3N drag
is an amount of force acting backwards.
Has a magnitude. For example speed.
Resultant force is the overall force acting in a direction on an object. It is best explained by digrams which show that the resulatnt force is the overall force given individual forces acting along a line.
unbalanced force and aceleration
force = mass × acceleration
F = m × a
weight, mass and g
weight = mass × g
W = m × g
falling and terminal velocity
When first an object is falling it is accelerating- the force acting downward (gravity) is larger than the force acting upwards (air resistance.) But when air resistance and gravity become equal the object will have reached its maximum speed; its terminal velocity.
effect of surface area (parachutes)
Dropping parachutes from a given height; this shows us that gravity is acting on them. By increasing the size of the parachute and recording the results we can see that air resistance also has an effect on falling objects; plotting a graph should reveal that bigger surface area takes more time, from which we can infer that air resistance acts on the falling objects.
factors effecting stopping distance
The condition of the driver; drugs/ tiredness (thinking distance)
How worn the brakes/ tyres are
If the weather conditions are poor
How heavy the car is
The speed the car is travelling at
Mass, momentum, velocity
momentum = mass x velocity
momentum and safety
force felt= change in momentum/time
If the time taken for momentum to change is increased
the overall force felt is decreased.
crumple zones and airbags increase time taken for the change in momentum to take place. Reducing the Force
Newton's third law
every force has an equal and opposite reaction
The equation of a moments is: moment= force x distance from pivot
It is important to remember that if the straight line is balanced then the clockwise and anti-clockwise moments will be exactly the same.
Elastic behaviour is the way that when you stretch an object with this behaviour it will return to its origional shape after the forces stretching it stop stretching it.
Note that if you stretch an elastic band to far it won't go back? this is because it as reached its elastic limit which, beyond this point, means it looses its elastic behaviour.
Gravitational field strength
Gravitational field strength is how strongly something pulls an object towards it.
Earth has a higher gravitational field strength than the moon: on earth we are pulled down so much that we can jump only for a few seconds; on the moon the time you can jump for is longer as it is pulling you back in with a weaker gravitational field.
The reason for this difference is mass, the earth has more mass than the moon and so has a bigger gravitational field strength. Bigger planets than earth will have a higher gravitational field strength.
They all have elliptical orbits.
Comets and planets go round a star; moons go round planets.
Comets have more elongated orbits.
The universe contains many galaxies.
Galaxies contain many stars, each star has a solar system.
Our solar system is an a galaxy called the milky way.
fields and orbits
If an object is within the field of another objects gravitational force then it will travel around it in a path known as an orbit.
moons to orbit planets
the planets to orbit the sun
artificial satellites to orbit the Earth
comets to orbit the sun
Orbital speed = 2× π ×orbital radius/ time period