P2 Forces

Volume is the amount of space contained in an object. Measuring cylinders are for volume

average speed (m/s) = total distance (m) / time taken (s)

acceleration (m/s²) = change in velocity (m/s) / time taken (s)

(Final speed)² - (Initial speed)² = 2 x acceleration x distance. v² - u² = 2as

Final speed = initial speed + (acceleration x time). v = u + at

Distance = (initial speed x time) + ½ (acceleration x time²). s = ut + ½ a t²

Distance is how far an object moves. A scalar quantity - contains a magnitude but not a direction.

Displacement is the distance an object moves in a straight line from a starting point to a finishing point. A vector quantity - contains a magnitude and a direction.

Speed is a scalar quantity - no direction only magnitude

Velocity describes an object’s direction as well as it’s speed. A vector - magnitude and direction

Vector quantities: acceleration, velocity, force, displacement

Scalar quantities: speed, distance, energy, temperature, mass

to add vectors , draw each vector as an arrow one after the other. The length of the arrow represents the magnitude of aa quantity. The direction of the arrow represents the direction of the vector quantity

Pythagoras theorem to work out the resultant force. (10² + 10²) = square root 200 = 14.1 N

Distance-time graphs have distance on the y-axis and time on the x-axis. on a distance-time graph, motion at a constant speed is shown by a straight line. if the line is horizontal then the object is stationary.

speed-time graphs have speed on the y-axis and time on the x-axis. if an objects speed is constant, then the speed-time graph will be horizontal. if the object is not moving, the graph will run along the x-axis. acceleration determines the change in speed. increase speed = positive gradient. decrease speed = negative gradient. a curved line shows the acceleration was not constant.

the area under a speed-time graph is equal to the distance travelled by an object. To find the area under the graph, break it down into shapes and add the areas

velocity is displacement over time

a force is a push or pull that acts on an object when it interacts with another object.

contact forces happen when two objects are physically touching. Friction, air resistance, tension and normal contact force.

non-contact forces happen when objects are separated. Gravitational force, electrostatic force and magnetic force.

Friction: whenever two surfaces are touching and try to move against each other. opposes their motion.

air resistance: when an object moves through air and collides with air molecules, slows the object down.

tension is the pulling force that a string of cable exerts when something or someone pulls on it.

Normal contact force: when you push on a table, your hand doesn’t move through it, this is because the normal contact forced from the table pushes equally on your hand.

Newton’s 1st law: the velocity of an object will only change if a resultant force is acting on the object. This applies to a stationary or moving object.

if an object is stationary and there is no resultant force acting on it, it will stay stationary

if an object is moving and there is no resultant force acting on it, the object will continue moving in the same direction at the same speed. same velocity.

Newton’s 2nd law: a force may cause a mass to accelerate. This acceleration can be a change in speed, a change in direction or a change in both speed and direction.

the resultant force is the sum of all of the forces acting on an object. the change in an object’s motion is caused by the resultant force. if the forces acting on an object are unbalanced it means that a resultant force is acting on the object.

Resultant force causes an acceleration

Resultant force (F) = mass (m) x acceleration (a)

Newton’s 3rd law: whenever 2 object’s interact, the forces that they exert on each other are equal and opposite. if one object exerts a force on another object, then the other object must be exerting a force back

a free body force diagram showing the forces acting on an object. These are shown as Vectors

the forces acting on a skydiver are air resistance and the skydivers weight

the forces acting on a driving car are the driving force, the normal contact force, the weight and friction.

resultant force 0 = equilibrium

accelerating car - resultant force upwards = 5000N -5000N= 0N. resultant force forwards = 3000N-1000N = 2000N. if the driving force is reduced to 1000N, the car is in equilibrium.

Mechanical: the work done by a force is equal to the energy transferred to the object.

Power = Watts

work done = force x distance = change in energy

power is the rate of energy transfer. The faster that energy is transferred, the higher the power. The more powerful a lightbulb is, the more light energy will be produced

we can stretch, bend or compress objects by applying forces to them. for this to happen there must be 2 or more forces acting on an object. if only one force is acting the object will just move in the direction of that force.

an elastically deformed object will return to it’s original shape when the force stops. a spring is an elastic object

an inelastically deformed object will not return to its original shape when the force stops. a car is an inelastic object

on an extension-load graph, the limit of proportionality is where the line begins to curve. force acting on a spring on the y-axis and the extension of the spring on the x-axis.

when a spring is stretched, the increase in the length of the spring is called extension.