a force is any push or pull forces can be contact forces that's when objects are physically touching like when you push a door or they can be non-c contact like magnetism electrostatic forces and gravity This Is A New Concept in gcsc physics and shocker it's a silly one because even contact forces are due to the electrostatic repulsion between electrons in your skin and the door for example but whatever technically pushing a door involves a normal contact force while other contact forces could be friction air resistance and tension the important thing is that we can represent forces with vectors that is an arrow that shows the direction and magnitude of the force the magnitude is the size of the force and that's indicated by the length of the arrow if two forces act on an object there's a resultant Force we find this by technically adding the vectors however if they're going in opposite directions one must be negative so in this case the resultant force would be 3 Newtons to the right and that's positive if we've decided that positive is in the right direction if vectors are at right angles to each other you use Pythagoras to find the resultant this works because you can make a triangle by moving one of the forces you could also be expected to use trig that's Soaker TOA to find either one of these angles chanar is going to be tan you use if any if forces are balanced that is they add up to zero that means that the object will not accelerate it won't change velocity no that doesn't necessarily mean it's not moving it just stays at a constant velocity and that could be 0 m/ second of course this is Newton's first law of motion by the way more those in a bit if a measurement or quantity just has magnitude but no direction it's not a vector but it's called a scalar instead here are some examples of both note that displacement is distance traveled with a direction while similarly velocity is the vector form of speed weight is another name for the force due to gravity that acts on an object it's calculated by multiplying the mass in kilograms by gravitational field strength or G which here on Earth is 9.8 Newtons per kilogram sometimes we just round up to 10 though you'll be told which to use in a question that means that 1 kilogram of Mass on Earth has a weight of 10 Newtons now if you hold an object up with your hand you must be pushing up with a force that is equal to its weight in order for the forces to be balanced and so it doesn't accelerate however that means that if you lift it upwards at a constant speed that's also true that's something that people often forget to lift something at a constant speed you must be lifting with a force that's the same as the weight we can therefore then calculate the energy that is used to lift this object using the equation for work work done that's work done equals force time distance moved work done is just a fancy term for energy transferred by a force this equation is true for any situation but in this case the force is the weight and the distance is the height so we could say the gain in energy is equal to mass * G * H does that look familiar it should because that's the exact same equation for calculating gravitational potential energy that's GP gained to be precise forces can also deform an object if you pull on a spring that is fixed at one end it will stretch or extend hooks law states that F equal ke that's Force equals spring constant sometimes called stiffness times extension the unit for spring constant is Newtons per meter this works for any object that stretches elastically that is returns to its original shape once the force is removed it can also be true if an object is compressed instead we can see that as K is a constant force and extension are directly proportional that means whatever happens to one happens to the other double the force double the extension you can hang varying masses off a spring and measure the extension and you'll end up with a straight line that goes through the origin 0 0 and that proves this directly proportional relationship if you carry out this experiment just make sure your ruler zero Mark is lined up with the bottom of the spring that way you can be sure you're only measuring extension rather than the length of the whole spring that would introduce a systematic error if you did that by mistake also make sure you're at ey level with the bottom of the spring when measuring against the ruler to a void Parallax error and that is a random error rather than a systematic error the energy stored in the spring is equal to half k^ s something was attached to the spring and you let go the object would gain the same amount of kinetic energy at least in an ideal or closed system that is no energy is lost of the surroundings due to heat for example just for Triple A Moment is a turning Force for example what you do with a spanner this is equal to force times distance to the pivot so the unit just ends up being newton meters note that this looks similar to the work done equation but this force and distance here are perpendicular to each other rather than parallel similarly to just normal forces if the moments turning clockwise are equal or balanced with the moments turning anticlockwise the object will not turn that is if it wasn't turning to begin with we can call this the principle of Moments by the way an application of moments is Gears a small gear can turn a large gear in order to increase the moment produced you can think of pressure as being how concentrated a forces the equation is pressure is equal to force divided by area so the unit for pressure is Newtons per met squar but we can also call this unit pascals or PA for short you probably know the deeper you go underwater the greater the pressure and this is due to the weight of the water above your head pushing down on you we can calculate this pressure using p equal H row that's just a Greek letter time g h being height of the water column above you basically depth time density time gravitational field strength the density of water is 1,000 kg per M cubed for gas pressure in paper 2 all you need to know is that it's due to the collisions of the gas particles with surfaces and you can hopefully remember from paper one that you can increase this by adding more gas reducing the volume or raising the temperature which makes the particles move faster all three of these result in the collisions occurring more frequently while increase in the temperature also means that the particles have more kinetic energy so they collide with the walls with more momentum therefore exerting a greater force more momentum in a bit the higher your altitude the less dense the atmosphere becomes due to there being fewer particles in in any given volume hence pressure also decreases back to double speed and velocity are measured in me/ second while velocity also has Direction so it could be positive or negative or up and down left and right here are some typical speeds for when you're traveling course speed and velocity are calculated by distance or displacement over time if you have a distance time graph the gradient of the graph gives you the speed or velocity if it's a curve just draw a tangent at the point you need to and find its gradient a speed or velocity time graph can give you even more information this time the gradient gives you change in speed divided by time which is acceleration here's the equation two the unit of acceleration is me/ second squared and it tells you how quickly speed is changing if it's a negative gradient heading to zero that means the object is decelerating slowing down however this graph can also go into negative values for example when a ball is thrown upward and comes back down in that case the velocity starts positive and fast but decreases to zero when it reaches the top where then turns around so the velocity becomes more negative as it falls incidentally this graph has a constant negative gradient gravity is accelerating it downwards at a constant rate even though its direction changes what you find is that for any object that's falling its acceleration is 9.8 m/s squared the same as gravitational field strength because they are the same thing a velocity time graph can also give you the distance traveled you get that by calculating the area under the graph any area under z m m/ second counts as negative displacement by the way that's why the area of both these triangles in this graph adds up to zero that makes sense though doesn't it seeing that it's gone back from whence it came I.E your hand suat or Newton's equations of motion are a way of predicting what an object will do if it's accelerating s is displacement U is initial velocity V is final velocity a is acceleration and T is time however AQA only give you one of these equations in the formula sheet and so that's really the only one that you will be expected to use U is zero if it starts at rest V equals z if an object is moving to begin with but then decelerates to a standstill for objects falling a is the same as G that's 9.8 m/s squar for any question involving one of these equations you write down your variables put a question mark next to what you're trying to find and put the values next to the other three that you've been given you can ignore the fifth unused variable depending on what data you're given you pick the correct equation with the four variables in rearrange it if necessary then just plug in your numbers we already know that Newton's first law is this when there's no resultant Force an object's motion is constant in other words no change in velocity that could be because there's no forces acting or the forces are balanced by the way inertia is the term we use to describe the tendency for an object's motion to stay constant unless acted on by a resultant Force Newton's Second Law involves unbalanced forces that is there is a resultant Force this is equal to ma masstimes acceleration that's all Newton's second law is fals ma only one of these can be true in any situation there's either no resultant force or there is we can prove Newton's second law by doing a practical we use a trolley on a track being pulled by the weight of masses hanging over a pulley on the end we can use light Gates photo gates to measure the acceleration between two points then change the weight on the string just remember that whatever Mass you take off the hanger must go on the trolley itself as the force is accelerating both the trolley and the masses themselves we draw a graph of force against acceleration and it should be a straight line through the origin proving the proportional relationship between F and a the gradient should give you the total mass of the trolley and slotted masses Newton's third law however is always true and this is the one that people get confused about understandably for every action of force there is an equal and opposite reaction force but this is not referring to balanced forces it's all about perspective when we think about the first two laws we only really consider the object itself for example the force pulling downwards on the ball is its weight even if there is air resistance there's a resultant Force downwards however if you zoom out and think about the Earth too well we know that the Earth is pulling down the ball but Newton's third law says the complete opposite is true as well the ball is also pulling the Earth up now the Earth is so massive that it doesn't really have an effect but it's still true nevertheless another example if you have two ice Gators if the guy skater pushes on the girl skater there's an equal and opposite reaction force pushing back on him too that's why they both move away from where they were the overall stopping distance for a car is a result of the thinking distance that's how far you go before you react to seeing the Bunny and the braking distance after you slammed on the brakes if you double your speed you double your thinking distance because you travel twice as far in the time it takes for you to react makes sense however doubling your speed quadruples your breaking distance because your car needs to lose all of its kinetic energy which is equal to half MV squared well that means that if you double the V * 2^ 2 is Time 4 if you triple your speed kinetic energy goes up by time 9 so that means so does your braking distance other factors that affect thinking distance are distractions alcohol drugs whereas braking distance can be affected by the condition of your brakes the tires the road the weather Etc the faster you go the more moment momentum you also have momentum is similar to inertia you can think of it as being a measure of how hard it is to get something to stop here's the equation momentum is equal to mass times velocity the unit therefore is kilogram m/s momentum is a vector which means you have negative momentum if your velocity is negative in a collision kinetic energy isn't always conserved but total momentum always is that means whatever the total momentum of the objects was before there must be the same total momentum afterwards as well calculations on this can be tricky but you just have to be careful with your pluses and minuses you write down M1 U1 if there's just one object moving to begin with remember U from suat we can use it here too and on M2 U2 if there's a second object moving too this then is the total momentum before the Collision before the event this could also be zero if nothing's moving to begin with say a cannon about to fire then all we have to say is that this is equal to the total momentum afterwards M1 V1 for one object plus M2 V2 if there's second object moving to if they've coupled together we just say m * V where m is the total mass of the two then all you have to do is pop your numbers in making sure that everything traveling to the left say has a negative velocity and you'll be left with one unknown rearrange to find it you get your answer incidentally in the case of the Cannon as there's zero total momentum before the same must be true after too even though the cannon ball is moving that must mean the cannon has the same momentum but in the opposite direction so they still add up to Z Z this is an example of recoil just for triple force and momentum are closely linked Newton's second law says that F equal ma but we also know that a is equal to Delta V / T so actually it's also true that force is equal to change in momentum over time or we can say the rate of change of momentum the shorter the time taken for momentum to change the bigger the force needed or felt that's why we use seat belts airbags and crumble zones in cars your change in momentum is the same when you use them but the increase the time taken for this to happen so a smaller force is felt you're more likely to survive it's just two ways of looking at forces the bigger the force the faster the acceleration or deceleration and so that also means the faster momentum changes too so I hope you found that helpful leave a like if you did and pop any questions or comments below I'll see you in the next video