Forces

• Force is a vector quantity with both magnitude and direction.
• Many physical quantities are vector quantities including force, velocity, displacement, and acceleration.
• Some physical qualities are scalar quantities with no direction such as speed, distance, mass, temperature, and time.
• Bike helmets contain a crushable layer of foam, lengthening the time taken for your head to stop, reducing impact on your brain.
• Crash mats and cushioned playground flooring increase time to stop if you fall on them, as they are made of soft, compressible materials.
• Vectors are usually represented by an arrow, with the length of the arrow showing the magnitude and the direction of the arrow showing the direction of the quantity.
• Velocity is a vector quantity, but speed is a scalar quantity.
• Both bikes are travelling at the same speed, but have different velocities because they are travelling in different directions.
• A force is a push or pull on an object that is caused by it interacting with something.
• All focus are either contact or non-contact forces.
• If the objects do not need to be touching, it is non-contact force such as magnetic force.
• When two objects interact, there is a force produced on both objects.
• An interaction pair is a pair of forces that are equal and opposite and act on two interacting objects.
• Gravity attracts all masses, but is only noticeable when the mass is really big-a planet.
• Anything near a planet or a star is attracted to it very strongly.
• On the surface of a planet it makes all things fall to the ground.
• Gravity gives everything a weight.
• Mass is the amount of “stuff” in an object-this is the same value for a given object anywhere.
• Weight is the force acting on an object due to gravity.
• Different sized gears can be used to change the moment of the force, with a force transmitted to a larger gear causing a bigger moment.
• Levers increase the distance from the pivots at which the force is applied, meaning less force is needed to get the same moment.
• Gears are circular discs with “teeth” around their edges, used to transmit the rotational effect of a force from one place to another.
• Distance is how far an object has moved, it’s scalar, while displacement is a vector, measuring the distance and direction in a straight line from the start to the finish.
• Fluids are substances that can flow because their particles are able to move around, exerting a pressure on the object they collide with.
• If the total anticlockwise moment equals the total clockwise moment about a pivot, the object is balanced and won’t turn.
• Upthrust is the force exerted by a fluid when an object is submerged in it, equal to the weight of fluid that is displaced by the object.
• Speed is how fast you’re going, while velocity is speed in a given direction.
• When an object is submerged in a fluid, the pressure of the fluid exerts a force on it from every direction, increasing with depth.
• Atmospheric pressure is created on a surface by air molecules colliding with the surface, decreasing with altitude.
• An object can be travelling at a constant speed with a changing velocity, when an object is changing direction while staying the same speed.
• Density is a measure of the “compactness” of a substance, with a denser substance having more particles in a certain space and exerting a higher pressure.
• The strength of the gravitational field varies with location-it’s stronger the closer you are to the mass causing the field, and stronger for larger masses.
• The weight of an object depends on the strength of the gravitational field at the location of the object.
• If you double the mass of an object, the weight doubles too-they are directly proportional.
• A resultant force is the overall force on a point or object.
• If you have a number of forces acting at a point you can replace them with a single force (with the same effect as all the original forces together) this single force is called the resultant force.
• Work done is the same as the energy transferred.
• W=Fs (work done (J)=Force (N) x distance (m))
• The force causing the change is equal to the rate of change of momentum.
• Momentum is a vector quantity, represented by the equation Momentum=Mass x Velocity.