![]() the tyres getting squashed where they contact the ground, or when the soft ground gets pushed out of place). This force is mainly due to the deformation of the ground and the object (e.g. The force is opposite to the direction of movement. '''Rolling resistance due to the ground''' – This occurs for rolling objects. If the grip is insufficient, then the object would slip on the ground (think about trying to accelerate a car when the wheels are stuck in the mud). To increase traction, the object needs to push backwards on the ground more strongly – in a car this means pressing down on the accelerator, on a bike this means pushing on the pedals more strongly.įor traction force to occur there needs to be sufficient grip between the object and the ground to prevent the wheel sliding. This is the forward force on cars, bikes, walkers, runners, because to get a forward motion, all these objects need to push back on the ground. '''Traction force due to the ground''' – This occurs when the object pushes backwards on the ground, therefore the ground creates a forward force on the object. ![]() a tension force would cause a rope to go from slack to tense. '''Tension Force:''' the pull force associated with the stretching of an object. the upwards force on a boat is “buoyancy force due to the water”. '''Buoyancy force due to liquid or gas''' – This is the force that allows things to float in gas or liquid. ![]() Thrust force due to water occurs for swimmers and boats, because the object pushes water backwards. Thrust force due to gases occurs for rockets, since the engines push burning gas out. Thrust force due to air occurs for planes, since the propellers or jet engines force air backwards. '''Thrust force due to a gas or liquid''' – A thrust force occurs when a gas or liquid is being pushed backwards by the object, which means the gas or liquid pushes the object forwards. It does NOT occur for all objects in the air, e.g. Lift force occurs for planes, birds and gliders because they have wings that have the correct angle to push the air downwards. '''Lift force due to the air''' – this force occurs when the shape of the object results in the air being deflected downwards, therefore the air pushes the object upwards. '''''Note: This force occurs whenever the object is moving relative to the gas or liquid – for example, if you are standing still on a windy day, you can still say you have drag due to the air.''''' The direction of drag is opposite to the motion. For example a swimmer has drag due to water, and a runner has drag due to air. '''Drag due to a gas or liquid OR resistance force due to a gas or liquid''' – This occurs when an object is moving through the gas or liquid. The friction force increases with greater contact area between surfaces and roughness of surfaces.''''' When friction does cause motion in these cases the forward friction force can be called “traction”. '''''Note: It is incorrect to say “friction opposes motion” because in many situations it is the friction force that is creating motion, for example when people walk or cycle. If the two surfaces are sliding past each other the friction is in the opposite direction to the sliding. The correct way to describe friction is that '''FRICTION OPPOSES SLIDING'''. '''Friction due to the ground''' – (or due to whatever surface the object is on): Friction always occurs when two solid surfaces are sliding past each other. This means when the ground is horizontal, the support force is directly upwards. The direction of the support force is at right angles to the surface. '''Support force due to the ground''' - (or due to whatever surface the object is on): Support force occurs when two solid surfaces are touching each other. This is the same kind of force as the push force, but the force acts towards the object doing the pulling. ![]() '''Pull force due to another object''' – E.g. The push force disappears as soon as the person loses contact. This force acts away from the object doing the pushing. ![]() '''Push force due to another object''' – E.g. The size of a force is measured in '''Newtons (N)''' or in SI Base units, '''kgms^-2^''' Sometimes this change in motion can cause the object to deform or change its shape. ![]()
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