Effects and Uses of Forces

Key Issues

Titles

Chapters

• Acceleration
• appreciate that, in the absence of all other forces, objects near the surface of the earth fall with the same acceleration and recall that this acceleration is known as the acceleration of free fall
• At equilibrium, the sums of clockwise and anticlockwise moments balance
• Atoms
• calculate the moment of a force as force times perpendicular distance from the pivot
• Centripetal Force
• Changes in Momentum
• Circular Motion
• describe some examples of circular motion
• describe some practical applications of levers
• Difference between speed and velocity
• Distance-time graphs
• distinguish between distance and displacement, speed and velocity
• distinguish between mass and weight, in that, mass is an unchanging property of an object whereas weight is a force that depends on how strong gravity is
• Equation of Force and Momentum
• Equation of Momentum
• Force, change in momentum and time taken for the change are related by the equation: force (newton, N) = change in momentum (kilogram metre/second, kg(m/s)) / time taken for the change (second, s)
• Forces and moving objects
• Gaining and Losing Energy
• Gas particles exert a force on their container
• If a body is not turning, the total clockwise moment must be exactly balanced by the total anticlockwise moment about any axis
• If suspended, a body will come to rest with its centre of mass directly below the point of suspension
• If the line of action of the weight of a body lies outside the base of the body there will be a resultant moment and the body will tend to topple
• INTERACTIONS BETWEEN OBJECTS
• investigate experimentally the relationship between force and the extension of a helical spring
• Momentum has both magnitude and direction
• Momentum in a Collision
• Momentum is conserved in any collision/explosion provided no external forces act on the colliding/exploding bodies
• Momentum, mass and velocity are related by the equation: momentum (kilogram metre/second, kg m/s) = mass (kilogram, kg) x velocity (metre/second, m/s)
• Origins of Forces
• recall and use the quantitative relationships between average speed, distance and time, including the calculation of average speed from linear distance-time graphs
• recall and use the quantitative relationships between displacement, time and average velocity
• recall and use the quantitative relationships between force, mass and acceleration in the form F = ma, where F is the resultant force
• recall and use the quantitative relationships between initial velocity, final velocity, acceleration and time. (Problems will only be set on motion in one direction. Equations of motion will not be examined.
• recall and use the quantitative relationships between pressure, force and area; recall that pressure is measured in Pascals. (Problems may be set in which N/cm2 and N/mm2 are used. There will be no interchange of units)
• recall that an object moving in a circle requires a force and that this force acts towards the centre of the circle
• recall that if this force is removed the object will fly off at a tangent to the circle
• recall that momentum is the product of mass and velocity
• recall that the slope of a displacement-time graph is the velocity and that the slope of a velocity-time graph is the acceleration and that the area under the graph is the displacement
• recall that, on the Earth, gravity exerts a force of 10 N on every kilogramme of mass and be able to carry out simple calculations involving mass and weight
• recognise and use the equation: weight = mass × acceleration of free fall
• Recognise the factors that affect the stability of a body
• Stability
• state and use Hooke's Law and use it to solve simple problems
• state the principle of moments and use it to solve simple problems. Calculations limited to two forces other than that acting at the pivot. Perpendicular distances only will be given
• The Centre of Mass
• The centre of mass of a body is that point at which the mass of the body may be thought to be concentrated
• The centre of mass of a symmetrical body is along the axis of symmetry
• The centripetal force needed to make a body perform circular motion increases as: the mass of the body increases; the speed of the body increases; the radius of the circle decreases
• THE EFFECT OF FORCES
• The Moment
• The resultant force causing this acceleration is called the centripetal force. The direction of the centripetal force is always towards the centre of the circle
• The size of the moment is given by the equation: moment (newton metre, Nm) = force (newton, N) x perpendicular distance from the line of action of the force to the axis of rotation (metre, m)
• The turning effect of a force is called the moment
• The variation of extension with applied force in springs and rubber bands
• Turning effects and moments of forces
• understand the meaning of elastic limit
• understand the term centre of mass and how the stability of an object depends on the position of the centre of mass and the width of its base
• use graphical methods to determine velocity, acceleration and displacement
• When a body moves in a circle it continuously accelerates towards the centre of the circle. This acceleration changes the direction of motion of the body, not its speed
• When a force acts on a body that is moving, or able to move, a change in momentum occurs