# Forces & Motion

Everything you need to know

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• Forces & Motion
• Distance and Velocity Time Graphs
• Distance Time Graphs
• Calculating speed from graph
• Flats shows stopped
• Steeper part is faster
• curves show acceleration or deacceleration
• curve starting to level off means slowing down
• Velocity Time Graphs
• Calculating acceleration from a velocity time graph
• Terminal Velocity
• Free- Fallers reach terminal Velocity
• 1.When free falling objects first set off, they have much more force accelerating then resistance slowing them down.
• 2.As the velocity, increase it builds resistance slowing them down
• 3. The acceleration gradually slows down until both acceleration and resistance forces are equal. This is terminal velocity
• Newtons Three Laws of Motion
• First Law
• Law: Balanced forces mean no change in velocity
• As long as all the forces are balanced it stays still
• Second Law
• Law: A resultant Force means acceleration
• If there is an unbalanced force, then the object will accelerate in that direction
• Third law
• If object A exerts a force on object B then object B exerts the exact opposite force on Object A
• Law: Reaction Forces
• Resultant Force
• To work it out use: Force= mass x acceleration
• Momentum
• Meaning: Momentum is conserved when no external factors act. The total momentum after is the same as it was before
• Calculating Momentum use: Momentum= Mass x Velocity
• Force causes changes in Momentum
• Formula: Force Acting (N)= Change in Momentum/Time taken for change to happen
• Acceleration
• Speed Formula Speed= Distance/  time
• Only use this formula when speed is constant
• Calculating Acceleration
• Formula: Acceleration= change in velocity/ Time Taken
• Remember: Change in velocity is final velocity minus initial velocity
• Acceleration is how quickly the velocity is chaging
• Turning Forces
• A Moment is the turning effect of a force
• The force on the spanner causes a turning effect or moment on the nut. A larger force would mean a larger momentum
• Formula: Moment= Force x perpendicular distance (m) between line of action and pivot
• The centre of gravity hangs directly below point of suspension
• Principle of Moments
• Question of Balance- Are the moments equal
• The Answer: If an object is balanced then: Total Anticlockwise Moments= Total clockwise moments
• Forces are not always equal across all support
• If a light rode is being supported at both ends, the upward force provided by each support, won't be  the same
• And if the Moments are not equal
• If the total anticlockwise moments do not equal the total clockwise moments, there will be a resultant moment
• Hooke`s Law
• Hooke's Law says that Extension is proportional to force.
• A metal spring will also obey hooke's Law,  if two opposite forces are applied to each end.
• Hooke's law stops working when the force is great enough
• A material can return to its original shape after an elastic deformation expect past hooke's Law
• Gravity and the Universe
• Our Solar System is in the Milky Way Galaxy
• Gravity provides the force that causes orbits
• It provides orbits which excist in:
• 1) Any object travelling in a circle is constantly charging direction
• 2) Any orbit is a balance between forward motion and backward motion
• 3)The planets move around the sun in almost a circular orbit.
• 4) Gravity is responsible for all our other planets in our solar system
• The moon orbits the earth. Other planets also have there own moons.
• Artificial Satellites that are made by man and launched into space.
• Comets are small lumps of icy rock orbiting the earth
• The Universe is a large collection of billions of Galaxies
• Orbital Speed
• Gravity decreases as you go further away
• There are different types of orbits:
• 1) Orbits of moons and planets
• 2)Comets orbit with very elliptical orbits
• 3)Comets have much longer than earth as it has to travel the outer edge of the solar system
• 4) Some artificial earth satellites have an orbital period of exactly one day
• Working out the speed of an Orbiting Object
• Step 1: Calculate the speed of an orbit using: Speed= Distance/time
• Step 2:For a circular orbit, the distance travelled is the circumference of the orbit, which to calculate distance= 2 x pie x radius of orbit
• Step 3- So the formula for speed of an orbit is: Orbital speed= (2 x pie x obital radius) / time period
• Vectors
• There are loads of different types of force
• Gravity and Weight
• Reaction Force
• Electrostatic Force
• Thrust
• Drag
• Lift
• Friction is always their to slow things down