Forces and motion

• Name Newtons 3 laws of motion

  Newton's 1st law tells us that an object won't change its motion unless acted upon by a force. Newton's 2nd law tells us that heavier objects need a larger force to move them (F=ma). Newton's 3rd law tells us that for every action there is an equal and opposite reaction. 
• types of forces

  
• what is the difference between Contact forces and non Contact forces


  Contact force occurs due to the contact between two different objects. Non-contact force occurs due to either attraction or repulsion between two objects such that there is no contact between these objects.

  
• A lorry has a mass of 7,500 kg. It travels south at a speed of 25 m/s. Calculate the momentum of the lorry.

  7500x25=187,500kg/ms
• an example of momentum....

  an elephant has no momentum when it is standing still. When it begins to walk, it will have momentum in the same direction as it is travelling. The faster the elephant walks, the larger its momentum will be.
• the momentum of an object depends only on its mass and velocity. If two objects have the same momentum, then they must have the same mass and velocity (or vice versa).
• what is momentum

  Momentum is the quantity that is used to describe the state of motion of an object with a non-zero mass. Hence, momentum is applicable to any moving object. 
• how does a change in momentum occur?


  When a force acts on an object that is moving, or able to move, there is a change in momentum:
• hookes law: Extension happens when an object increases in length, and compression happens when it decreases in length. The extension of an elastic object, such as a spring, is described by Hooke's law:

  force = spring constant × extension


  • force (F) is measured in newtons (N)
  • spring constant (k) is measured in newtons per metre (N/m)
  • extension (e), or increase in length, is measured in metres (m)
• A force of 3 N is applied to a spring. The spring stretches reversibly by 0.15 m - the fact that the string stretches reversibly means that it will go back to its normal shape after the force has been removed. Calculate the spring constant.


  (k=f/e) k=3/0.15=20n/m
• Gravitational fields definition

  All objects with mass produce a gravitational field. The more mass an object has, the greater its gravitational field will be.
• 9.8 is...

  the worlds acceleration due to gravity.
• what is the main law of momentum

  the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision.
• what is nuclear fission?


  Splitting of an atomic nucleus into two smaller nuclei.
• According to Newton's first law, what happens to an object traveling at a certain velocity?

  An object will continue to travel at that velocity unless acted upon by a resultant force.
• Explain why the pressure increases as more air is pumped into the tyre.

  more (air) particles (in the tyre) greater number of collisions with tyre (walls) per second
• The air pressure in a car tyre changes if the temperature of the air in the tyre increases. Explain why.

  (as temperature increases the) air particles have greater (mean) kinetic energy (so) more collisions with tyre (walls) per second (and) greater force in each collision greater (mean) force per square metre causes greater pressure (on wall of tyre)
• the resolution is the scale the coil is going up in, therefore 0.2 is the answer

  
• What is meant by ‘momentum is conserved’?

  the total momentum of a closed system remains constant before and after an event, as long as no external forces act on it.
• How do levers make work easier?

  Levers increase the distance from the pivot, reducing the force needed to move a load.
• An adult of mass 80 kg has more inertia than a child of mass 40 kg What is inertia?

  Inertia is the tendency of an object to resist changes in its motion. An object with more mass has greater inertia, meaning it is harder to start or stop moving.
• what is a moment?

  A moment is the turning effect of a force around a pivot. 
• What is the name of the force applied to a lever?

  Effort is the name of the force applied to a lever.
• how does 2 gears with one 2x as big as the other work?

  When two gears are connected, they rotate in opposite directions. If one gear is twice the size of the other:

  • The larger gear will rotate half as fast as the smaller gear.

  • The smaller gear will rotate twice as fast as the larger gear.

  • The larger gear provides more force, while the smaller gear provides more speed.

  
• what is one purpose of a gear?

  to transmit rotational force from one shaft to another. Gears are used to change the speed or direction of rotation, or to increase or decrease the torque applied to a shaft.
• what is torque?

  Torque is the rotational equivalent of force. It measures how effectively a force causes an object to rotate around a pivot.
• how does a lever make work easier?

   a lever makes work easier by changing the force applied to the machine or the distance over which the force is applied
• what forces act upon a car?

  1. Gravity – Pulls the car downwards.

  2. Normal force – The upward force from the ground, balancing gravity.

  3. Friction – Resists the motion of the car’s tires against the road.

  4. Air resistance (drag) – Opposes the car’s motion through the air.

  5. Driving force (thrust) – The force provided by the engine to move the car forward.
• what is the rule to know for momentum?

  the total momentum before the collision is equal to the total momentum after the collision
• Explain why the egg is less likely to break when dropped onto soft foam rather than onto a concrete floor.

  When the egg hits the soft foam, the impact time increases because the foam compresses. This reduces the rate of change of momentum, leading to a smaller force acting on the egg. In contrast, when dropped onto concrete, the impact time is very short, resulting in a large force, which is more likely to break the egg.
• What is the difference between scalar and vector quantities?

  Scalars have magnitude only.

  Vectors have magnitude and direction.
• name 3 vector quantities?

  Acceleration, velocity, force
• State Newton’s Third Law of Motion.

  every force has an equal opposite one
• Explain the changing motion of the skydiver in terms of the forces acting on the skydiver.

  The skydiver accelerates at first as weight is greater than air resistance. As velocity increases, air resistance builds up, reducing acceleration. Eventually, forces balance, and terminal velocity is reached. When the parachute opens, air resistance increases, causing rapid deceleration. As speed decreases, air resistance lessens until it balances weight again, reaching a slower terminal velocity before landing.
• The further a swimmer dives below the surface of the sea, the greater the pressure on the swimmer. Explain why.

  As depth increases, the weight of the water above the swimmer increases, exerting more force. Since pressure is caused by the force acting on a given area, the greater the depth, the greater the pressure.
• The force on the water causes an equal and opposite force to act on the boat. Which law is this an example of?

  Newton's third law 
• what is newtons 2nd law?

  the acceleration of an object is directly related to the net force and inversely related to its mass
• what is newtons 1st law of motion?

  An object remains at rest or moves at a constant velocity unless acted upon by an external force.
• Explain the effect of two other factors on the braking distance of a car.

  Factors= poor condition of tyres • poor road surface • wet or icy road Explanation= because of decreased friction

  Factors= increased mass of car

  Explanation= increases kinetic energy of car • more work needs to be done to stop car • increases momentum of the car
• what is meant by elastically deformed

  will return to its original shape/length when the force is removed