# Year 8 Forces

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# Year 8 Forces Learning Objectives Pupils should know:

• That speed is a measure of how far an object travels in a certain time
• Average Speed = distance ÷ time
• Speed is measured in units of metres per second (m/s)
• How to convert km/hr to m/s
• How to measure speed

• The difference between thinking distance and braking distance and factors that affect each.
• Be able to plot distance – time graphs
• Be able to calculate the speed from the gradient of a distance – time graph
• That acceleration is the rate of change of speed (velocity)
• Be able to plot speed time graphs
• Be able to calculate the distance travelled from the area under a speed time graph
• Describe how the forces acting on an object falling at terminal velocity are balanced
• That the area over which a force acts is important
• Pressure = Force ÷ Area
• That pressure is measured in Pascals (Pa) or N/m2 or N/cm2
• How to convert N/cm2 to N/m2
• Applications of high and low pressure
• That solids transmit force but fluids (liquids and gases) transmit pressure
• That in liquids:
a. Pressure increases with depth
b. Pressure acts equally in all directions
c. Pressure is the same at any depth
• How hydraulics use pressure
• That a force may cause an object to rotate or turn about a point called a pivot
• That the turning effect of a force is called the moment of the force
• That the size of the turning effect depends upon the size of the force and the distance of the force from the pivot
• Moment = force x distance to pivot
• Moment is measured in units Nm or Ncm
• That a moment may cause an object to rotate clockwise or anticlockwise
• How to calculate the result of two or more moments applied to an object
• That in equilibrium clockwise moments = anticlockwise moments
• Some applications of moments such as levers and cranes

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