Physics GCSE Module 2

• Force = mass x acceleration
• Gravity, magnetism and electrical charges cause forces
• Measured in newtons
• Measured with a newtonmeter
• Can push or pull
• Forces affect the movement of an object
• If the forces acting on an objest are equal (or balanced) then the object will stay as it is
• If the forces acting on an object are unequal (or unbalanced) then the object will move

Newtons Ideas

Newton sorted out a lot of ideas about foces and produces three laws:

• When one object exerts a force on another, the second object exerts an equal and opposite force on the first (often called  a newton pair)
• When the forces on something are balanced, it stays still or it keeps moving with a constant velocity (same speed in a straight line)

If the forces are unbalanced the velocity will change.

• A stationary object accelerates in the direction of the force
• A moving object speeds up, slows down or changes direction, depending on the unbalanced (or resultant) force

Speed

• Speed = distance / time

Distance / Time graph

• Straight line = steady speed
• Steep line = fast
• Horizontal line = stopped / stationary
• Gently gradient = slow

• When the speed of something moving increases, we say it accelerates
• When it slows down we say it deccelerates
• A change in direction also counts as acceleration, because the velocity is changed
• To calculate the acceleration we work out how much the speed increases each second
• Acceleration = change in velocity / time taken
• A straight line graph through the origin shows that the acceleration is directly porportional to the force
• A (alpha) F means porportional to
• 1 newton is the force that makes 1kg accelerate at 1m/s squared

When a driver sees a hazard she takes a short time to react (about 0.7s) and then does an emergency stop.

• The thinking distance, which is how far the vehicle travels as the driver reacts
• The breaking distance, which is how far the vehicle travels as is slows to a stop
• Thinking distance is increased be tiredness, alcohol (and other drugs), and distractions.
• Breaking difference is increased if the road is wet, or icy, or if the vehicle has worn breaks or worn tyres
• Speed also makes a difference

Spring behavior

• A spring is a good example of elastic behavior, it stretches when loaded, and returns to its original length when the load is removed

Hookes law

• Hookes law is F = k x e (F = force, k = constant, and e = extention)

Kinetic Energy

• Kinetic energy is the energy a moving object has
• It depends on the mass and the speed

Gravitational Potential Energy

When things are lifted up, they gain gravitational potential energy. When they fall they lose their gravitational potential energy.

• To work out the gravitational potential energy gained we use: Gravitational Potential Energy = Weight x Height Gained (J = N x m)
• Also Weight = Mass x Gravitational Field Strength (N = kg x N)

Momentum

• Momentum = mass x velocity (kg m/s = kg x m/s)
• We cannot make it or get rid of it - we can only transfer it
• Momentum before the event = momentum after the event